Systems and methods for health based spillover

ABSTRACT

The present solution provides a spillover management technique for virtual servers of an appliance based on health. Using a health based spillover technique, a network appliance may direct requests to a backup or second virtual server upon determining that a predetermined percentage of services being load balanced are down. In this manner, the spillover will occur based on a user controlled determination of a level of services being down to the number of services enabled. Instead of waiting for a last service of a virtual server to be marked down to spillover to another virtual server, the spillover may occur based on a user specified percentage. For example, the appliance may spillover from one virtual server to another virtual server when the number of services marked down relative to the number of enabled services falls below a specified percentage.

RELATED APPLICATIONS

This applications claims priority to and is a continuation of U.S. patent application Ser. No. 12/277,641, titled “Systems and Methods for Health Based Spillover” filed Nov. 25, 2008 of which is hereby incorporated in its entirety.

FIELD OF THE INVENTION

This application relates to computer networking technologies, and more specifically, to providing dynamic virtual server spillover management based on health.

BACKGROUND OF THE INVENTION

Network appliances are often used to provide access to one or more network services. A network appliance may comprise a number of virtual servers, each virtual server providing access to a number of services. The virtual servers may manage incoming connections from clients, and direct client requests to one or more services. In the course of managing incoming connection requests, network appliances may provide load balancing among the backend servers. When a virtual server is down or unavailable to service a connection request, the appliance may use a backup virtual server to manage incoming connections.

A virtual server may be operational but not operating at a desired performance level. A network appliance may direct a client request or connection to a virtual server which provides load balancing of a service available via multiple servers. If the service on each of the servers is down or unavailable, then the virtual server is not able to forward or load balance a request from a client. At that point, the network appliance may switch over to a backup virtual server providing access to and load balancing a second of set of servers to provide the service.

SUMMARY OF THE INVENTION

The present solution provides a spillover management technique for virtual servers of an appliance based on health. Using a health based spillover technique, a network appliance may direct requests to a backup or second virtual server upon determining that a predetermined percentage of services being load balanced are down. In this manner, the spillover will occur based on a user controlled determination of a level of services being down to the number of services enabled. Instead of waiting for a last service of a virtual server to be marked down to spillover to another virtual server, the spillover may occur based on a user specified percentage. For example, the appliance may spillover from one virtual server to another virtual server when the number of services marked down relative to the number of enabled services falls below a percentage, such as 50%.

In one aspect, the present invention relates to a method for an appliance to direct requests of a first virtual server managing a first plurality of services to a second virtual server upon determining a health of the first virtual server falls below a health threshold. The method includes an appliance identifying a health threshold for a first virtual server, the first virtual server directing requests from a plurality of clients to a plurality of services. The health threshold may be a percentage. The appliance monitors a status of multiple services, each with an assigned weight. In some embodiments, each of the services may be assigned a different weight. The appliance establishes a health for the services by summing weights of each of the services identified via monitoring as up and dividing the summed weights by a sum of weights of each of the services identified as enabled. The appliance determines that the health falls below the health threshold and responsive to the determination uses a second virtual server for directing the requests from the plurality of clients to a second plurality of services. The appliance responsive to the determination may direct client requests to the second virtual server instead of the first virtual server.

The appliance, in some embodiments, identifies the second virtual server as a backup virtual server for the first virtual server. In one embodiment, the appliance establishes the second virtual server in response to the determination. The appliance may monitor the status of the plurality of services of the first virtual server at a predetermined frequency. Also, the appliance may reestablish or redetermine the health upon a change to the status of one or more of the services. Responsive to changing a weight of one or more of the service, the appliance may reestablish or redetermine the health. In some embodiments, the appliance identifies the status of one or more of the services as disabled and excludes the one or more services in establishing the health. In another embodiment, the appliance identifies the status of one or more of the plurality services as up and determines the health exceeds the health threshold.

In another aspect, the present invention is related to a system to direct requests of a first virtual server managing a first plurality of services to a second virtual server upon determining a health of the first virtual server falls below a health threshold. The system includes a first virtual server configured with a health threshold, the first virtual server directing requests from clients to services. The health threshold is configured as a percentage. One or more monitors of the system monitor the status of each of the services, with each service assigned a weight. In some cases, one or more of the services is assigned a different weight. A health monitor establishes a health for the virtual server by summing weights of each of the services identified via monitoring as up and dividing the summed weights by a sum of weights of each of the services identified as enabled. The health monitor determines that the health falls below the health threshold and responsive to the determination, a connection manager uses a second virtual server for directing the requests from the clients to a second set of services. The connection manager, responsive to the determination, may direct client requests to the second virtual server instead of the first virtual server.

In some embodiments, the second virtual server is identified as a backup virtual server for the first virtual server. The second virtual server may be established responsive to the determination. The one or more monitors may monitor the status of the services of the first virtual server at a predetermined frequency. The health monitor may reestablish the health upon a change to the status of one or more of the services. The health monitor may reestablish the health upon a change to a weight assigned to a service. The one or more monitors identify the status of one or more of the services as administratively disabled and the health monitor excludes the one or more of the plurality of services in establishing the health. In some embodiments, the appliance identifies the status of one or more of the plurality services as up and determines the health exceeds the health threshold.

The details of various embodiments of the invention are set forth in the accompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment for a client to access a server via an appliance;

FIG. 1B is a block diagram of another embodiment of a network environment for delivering a computing environment from a server to a client via a plurality of appliances;

FIG. 1C is a block diagram of another embodiment of a network environment for delivering a computing environment from a server to a client via one or more different appliances;

FIG. 1D is a block diagram of an embodiment of an environment for delivering a computing environment from a server to a client via a network;

FIGS. 1E and 1F are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance for processing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of an appliance for optimizing, accelerating, load-balancing and routing communications between a client and a server;

FIG. 3 is a block diagram of an embodiment of a client for communicating with a server via the appliance;

FIG. 4A is one embodiment of a network of appliances for load balancing resources across branch offices;

FIG. 4B is a block diagram of an appliance using a plurality of monitoring agents to monitor a network service;

FIG. 5A is an embodiment of an appliance for providing a technique of virtual server spillover management based on health; and

FIG. 5B is a flow diagram of steps of an embodiment of a method for practicing a technique of spillover management based on health in conjunction with the system of FIG. 5A.

The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of reading the description of the various embodiments of the present invention below, the following descriptions of the sections of the specification and their respective contents may be helpful:

-   -   Section A describes a network environment and computing         environment useful for practicing an embodiment of the present         invention;     -   Section B describes embodiments of a system and appliance         architecture for accelerating delivery of a computing         environment to a remote user;     -   Section C describes embodiments of a client agent for         accelerating communications between a client and a server;     -   Section D describes embodiments of systems and methods for         dynamic load balancing; and     -   Section E describes embodiments of systems and methods for         health based spillover among virtual servers.         A. Network and Computing Environment

Prior to discussing the specifics of embodiments of the systems and methods of an appliance and/or client, it may be helpful to discuss the network and computing environments in which such embodiments may be deployed. Referring now to FIG. 1A, an embodiment of a network environment is depicted. In brief overview, the network environment comprises one or more clients 102 a-102 n (also generally referred to as local machine(s) 102, or client(s) 102) in communication with one or more servers 106 a-106 n (also generally referred to as server(s) 106, or remote machine(s) 106) via one or more networks 104, 104′ (generally referred to as network 104). In some embodiments, a client 102 communicates with a server 106 via an appliance 200.

Although FIG. 1A shows a network 104 and a network 104′ between the clients 102 and the servers 106, the clients 102 and the servers 106 may be on the same network 104. The networks 104 and 104′ can be the same type of network or different types of networks. The network 104 and/or the network 104′ can be a local-area network (LAN), such as a company Intranet, a metropolitan area network (MAN), or a wide area network (WAN), such as the Internet or the World Wide Web. In one embodiment, network 104′ may be a private network and network 104 may be a public network. In some embodiments, network 104 may be a private network and network 104′ a public network. In another embodiment, networks 104 and 104′ may both be private networks. In some embodiments, clients 102 may be located at a branch office of a corporate enterprise communicating via a WAN connection over the network 104 to the servers 106 located at a corporate data center.

The network 104 and/or 104′ be any type and/or form of network and may include any of the following: a point to point network, a broadcast network, a wide area network, a local area network, a telecommunications network, a data communication network, a computer network, an ATM (Asynchronous Transfer Mode) network, a SONET (Synchronous Optical Network) network, a SDH (Synchronous Digital Hierarchy) network, a wireless network and a wireline network. In some embodiments, the network 104 may comprise a wireless link, such as an infrared channel or satellite band. The topology of the network 104 and/or 104′ may be a bus, star, or ring network topology. The network 104 and/or 104′ and network topology may be of any such network or network topology as known to those ordinarily skilled in the art capable of supporting the operations described herein.

As shown in FIG. 1A, the appliance 200, which also may be referred to as an interface unit 200 or gateway 200, is shown between the networks 104 and 104′. In some embodiments, the appliance 200 may be located on network 104. For example, a branch office of a corporate enterprise may deploy an appliance 200 at the branch office. In other embodiments, the appliance 200 may be located on network 104′. For example, an appliance 200 may be located at a corporate data center. In yet another embodiment, a plurality of appliances 200 may be deployed on network 104. In some embodiments, a plurality of appliances 200 may be deployed on network 104′. In one embodiment, a first appliance 200 communicates with a second appliance 200′. In other embodiments, the appliance 200 could be a part of any client 102 or server 106 on the same or different network 104,104′ as the client 102. One or more appliances 200 may be located at any point in the network or network communications path between a client 102 and a server 106.

In some embodiments, the appliance 200 comprises any of the network devices manufactured by Citrix Systems, Inc. of Ft. Lauderdale Fla., referred to as Citrix NetScaler devices. In other embodiments, the appliance 200 includes any of the product embodiments referred to as WebAccelerator and BigIP manufactured by F5 Networks, Inc. of Seattle, Wash. In another embodiment, the appliance 205 includes any of the DX acceleration device platforms and/or the SSL VPN series of devices, such as SA 700, SA 2000, SA 4000, and SA 6000 devices manufactured by Juniper Networks, Inc. of Sunnyvale, Calif. In yet another embodiment, the appliance 200 includes any application acceleration and/or security related appliances and/or software manufactured by Cisco Systems, Inc. of San Jose, Calif., such as the Cisco ACE Application Control Engine Module service software and network modules, and Cisco AVS Series Application Velocity System.

In one embodiment, the system may include multiple, logically-grouped servers 106. In these embodiments, the logical group of servers may be referred to as a server farm 38. In some of these embodiments, the serves 106 may be geographically dispersed. In some cases, a farm 38 may be administered as a single entity. In other embodiments, the server farm 38 comprises a plurality of server farms 38. In one embodiment, the server farm executes one or more applications on behalf of one or more clients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more of the servers 106 can operate according to one type of operating system platform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond, Wash.), while one or more of the other servers 106 can operate on according to another type of operating system platform (e.g., Unix or Linux). The servers 106 of each farm 38 do not need to be physically proximate to another server 106 in the same farm 38. Thus, the group of servers 106 logically grouped as a farm 38 may be interconnected using a wide-area network (WAN) connection or medium-area network (MAN) connection. For example, a farm 38 may include servers 106 physically located in different continents or different regions of a continent, country, state, city, campus, or room. Data transmission speeds between servers 106 in the farm 38 can be increased if the servers 106 are connected using a local-area network (LAN) connection or some form of direct connection.

Servers 106 may be referred to as a file server, application server, web server, proxy server, or gateway server. In some embodiments, a server 106 may have the capacity to function as either an application server or as a master application server. In one embodiment, a server 106 may include an Active Directory. The clients 102 may also be referred to as client nodes or endpoints. In some embodiments, a client 102 has the capacity to function as both a client node seeking access to applications on a server and as an application server providing access to hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In one embodiment, the client 102 communicates directly with one of the servers 106 in a farm 38. In another embodiment, the client 102 executes a program neighborhood application to communicate with a server 106 in a farm 38. In still another embodiment, the server 106 provides the functionality of a master node. In some embodiments, the client 102 communicates with the server 106 in the farm 38 through a network 104. Over the network 104, the client 102 can, for example, request execution of various applications hosted by the servers 106 a-106 n in the farm 38 and receive output of the results of the application execution for display. In some embodiments, only the master node provides the functionality required to identify and provide address information associated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a web server. In another embodiment, the server 106 a receives requests from the client 102, forwards the requests to a second server 106 b and responds to the request by the client 102 with a response to the request from the server 106 b. In still another embodiment, the server 106 acquires an enumeration of applications available to the client 102 and address information associated with a server 106 hosting an application identified by the enumeration of applications. In yet another embodiment, the server 106 presents the response to the request to the client 102 using a web interface. In one embodiment, the client 102 communicates directly with the server 106 to access the identified application. In another embodiment, the client 102 receives application output data, such as display data, generated by an execution of the identified application on the server 106.

Referring now to FIG. 1B, an embodiment of a network environment deploying multiple appliances 200 is depicted. A first appliance 200 may be deployed on a first network 104 and a second appliance 200′ on a second network 104′. For example a corporate enterprise may deploy a first appliance 200 at a branch office and a second appliance 200′ at a data center. In another embodiment, the first appliance 200 and second appliance 200′ are deployed on the same network 104 or network 104. For example, a first appliance 200 may be deployed for a first server farm 38, and a second appliance 200 may be deployed for a second server farm 38′. In another example, a first appliance 200 may be deployed at a first branch office while the second appliance 200′ is deployed at a second branch office’. In some embodiments, the first appliance 200 and second appliance 200′ work in cooperation or in conjunction with each other to accelerate network traffic or the delivery of application and data between a client and a server

Referring now to FIG. 1C, another embodiment of a network environment deploying the appliance 200 with one or more other types of appliances, such as between one or more WAN optimization appliance 205, 205′ is depicted. For example a first WAN optimization appliance 205 is shown between networks 104 and 104′ and s second WAN optimization appliance 205′ may be deployed between the appliance 200 and one or more servers 106. By way of example, a corporate enterprise may deploy a first WAN optimization appliance 205 at a branch office and a second WAN optimization appliance 205′ at a data center. In some embodiments, the appliance 205 may be located on network 104′. In other embodiments, the appliance 205′ may be located on network 104. In some embodiments, the appliance 205′ may be located on network 104′ or network 104″. In one embodiment, the appliance 205 and 205′ are on the same network. In another embodiment, the appliance 205 and 205′ are on different networks. In another example, a first WAN optimization appliance 205 may be deployed for a first server farm 38 and a second WAN optimization appliance 205′ for a second server farm 38′

In one embodiment, the appliance 205 is a device for accelerating, optimizing or otherwise improving the performance, operation, or quality of service of any type and form of network traffic, such as traffic to and/or from a WAN connection. In some embodiments, the appliance 205 is a performance enhancing proxy. In other embodiments, the appliance 205 is any type and form of WAN optimization or acceleration device, sometimes also referred to as a WAN optimization controller. In one embodiment, the appliance 205 is any of the product embodiments referred to as WANScaler manufactured by Citrix Systems, Inc. of Ft. Lauderdale, Florida. In other embodiments, the appliance 205 includes any of the product embodiments referred to as BIG-IP link controller and WANjet manufactured by F5 Networks, Inc. of Seattle, Wash. In another embodiment, the appliance 205 includes any of the WX and WXC WAN acceleration device platforms manufactured by Juniper Networks, Inc. of Sunnyvale, Calif. In some embodiments, the appliance 205 includes any of the steelhead line of WAN optimization appliances manufactured by Riverbed Technology of San Francisco, Calif. In other embodiments, the appliance 205 includes any of the WAN related devices manufactured by Expand Networks Inc. of Roseland, New Jersey. In one embodiment, the appliance 205 includes any of the WAN related appliances manufactured by Packeteer Inc. of Cupertino, California, such as the PacketShaper, iShared, and SkyX product embodiments provided by Packeteer. In yet another embodiment, the appliance 205 includes any WAN related appliances and/or software manufactured by Cisco Systems, Inc. of San Jose, Calif., such as the Cisco Wide Area Network Application Services software and network modules, and Wide Area Network engine appliances.

In one embodiment, the appliance 205 provides application and data acceleration services for branch-office or remote offices. In one embodiment, the appliance 205 includes optimization of Wide Area File Services (WAFS). In another embodiment, the appliance 205 accelerates the delivery of files, such as via the Common Internet File System (CIFS) protocol. In other embodiments, the appliance 205 provides caching in memory and/or storage to accelerate delivery of applications and data. In one embodiment, the appliance 205 provides compression of network traffic at any level of the network stack or at any protocol or network layer. In another embodiment, the appliance 205 provides transport layer protocol optimizations, flow control, performance enhancements or modifications and/or management to accelerate delivery of applications and data over a WAN connection. For example, in one embodiment, the appliance 205 provides Transport Control Protocol (TCP) optimizations. In other embodiments, the appliance 205 provides optimizations, flow control, performance enhancements or modifications and/or management for any session or application layer protocol.

In another embodiment, the appliance 205 encoded any type and form of data or information into custom or standard TCP and/or IP header fields or option fields of network packet to announce presence, functionality or capability to another appliance 205′. In another embodiment, an appliance 205′ may communicate with another appliance 205′ using data encoded in both TCP and/or IP header fields or options. For example, the appliance may use TCP option(s) or IP header fields or options to communicate one or more parameters to be used by the appliances 205, 205′ in performing functionality, such as WAN acceleration, or for working in conjunction with each other.

In some embodiments, the appliance 200 preserves any of the information encoded in TCP and/or IP header and/or option fields communicated between appliances 205 and 205′. For example, the appliance 200 may terminate a transport layer connection traversing the appliance 200, such as a transport layer connection from between a client and a server traversing appliances 205 and 205′. In one embodiment, the appliance 200 identifies and preserves any encoded information in a transport layer packet transmitted by a first appliance 205 via a first transport layer connection and communicates a transport layer packet with the encoded information to a second appliance 205′ via a second transport layer connection.

Referring now to FIG. 1D, a network environment for delivering and/or operating a computing environment on a client 102 is depicted. In some embodiments, a server 106 includes an application delivery system 190 for delivering a computing environment or an application and/or data file to one or more clients 102. In brief overview, a client 10 is in communication with a server 106 via network 104, 104′ and appliance 200. For example, the client 102 may reside in a remote office of a company, e.g., a branch office, and the server 106 may reside at a corporate data center. The client 102 comprises a client agent 120, and a computing environment 15. The computing environment 15 may execute or operate an application that accesses, processes or uses a data file. The computing environment 15, application and/or data file may be delivered via the appliance 200 and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of a computing environment 15, or any portion thereof, to a client 102. In one embodiment, the appliance 200 accelerates the delivery of the computing environment 15 by the application delivery system 190. For example, the embodiments described herein may be used to accelerate delivery of a streaming application and data file processable by the application from a central corporate data center to a remote user location, such as a branch office of the company. In another embodiment, the appliance 200 accelerates transport layer traffic between a client 102 and a server 106. The appliance 200 may provide acceleration techniques for accelerating any transport layer payload from a server 106 to a client 102, such as: 1) transport layer connection pooling, 2) transport layer connection multiplexing, 3) transport control protocol buffering, 4) compression and 5) caching. In some embodiments, the appliance 200 provides load balancing of servers 106 in responding to requests from clients 102. In other embodiments, the appliance 200 acts as a proxy or access server to provide access to the one or more servers 106. In another embodiment, the appliance 200 provides a secure virtual private network connection from a first network 104 of the client 102 to the second network 104′ of the server 106, such as an SSL VPN connection. It yet other embodiments, the appliance 200 provides application firewall security, control and management of the connection and communications between a client 102 and a server 106.

In some embodiments, the application delivery management system 190 provides application delivery techniques to deliver a computing environment to a desktop of a user, remote or otherwise, based on a plurality of execution methods and based on any authentication and authorization policies applied via a policy engine 195. With these techniques, a remote user may obtain a computing environment and access to server stored applications and data files from any network connected device 100. In one embodiment, the application delivery system 190 may reside or execute on a server 106. In another embodiment, the application delivery system 190 may reside or execute on a plurality of servers 106 a-106 n. In some embodiments, the application delivery system 190 may execute in a server farm 38. In one embodiment, the server 106 executing the application delivery system 190 may also store or provide the application and data file. In another embodiment, a first set of one or more servers 106 may execute the application delivery system 190, and a different server 106 n may store or provide the application and data file. In some embodiments, each of the application delivery system 190, the application, and data file may reside or be located on different servers. In yet another embodiment, any portion of the application delivery system 190 may reside, execute or be stored on or distributed to the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 15 for executing an application that uses or processes a data file. The client 102 via networks 104, 104′ and appliance 200 may request an application and data file from the server 106. In one embodiment, the appliance 200 may forward a request from the client 102 to the server 106. For example, the client 102 may not have the application and data file stored or accessible locally. In response to the request, the application delivery system 190 and/or server 106 may deliver the application and data file to the client 102. For example, in one embodiment, the server 106 may transmit the application as an application stream to operate in computing environment 15 on client 102.

In some embodiments, the application delivery system 190 comprises any portion of the Citrix Access Suite™ by Citrix Systems, Inc., such as the MetaFrame or Citrix Presentation Server™ and/or any of the Microsoft® Windows Terminal Services manufactured by the Microsoft Corporation. In one embodiment, the application delivery system 190 may deliver one or more applications to clients 102 or users via a remote-display protocol or otherwise via remote-based or server-based computing. In another embodiment, the application delivery system 190 may deliver one or more applications to clients or users via steaming of the application.

In one embodiment, the application delivery system 190 includes a policy engine 195 for controlling and managing the access to, selection of application execution methods and the delivery of applications. In some embodiments, the policy engine 195 determines the one or more applications a user or client 102 may access. In another embodiment, the policy engine 195 determines how the application should be delivered to the user or client 102, e.g., the method of execution. In some embodiments, the application delivery system 190 provides a plurality of delivery techniques from which to select a method of application execution, such as a server-based computing, streaming or delivering the application locally to the client 120 for local execution.

In one embodiment, a client 102 requests execution of an application program and the application delivery system 190 comprising a server 106 selects a method of executing the application program. In some embodiments, the server 106 receives credentials from the client 102. In another embodiment, the server 106 receives a request for an enumeration of available applications from the client 102. In one embodiment, in response to the request or receipt of credentials, the application delivery system 190 enumerates a plurality of application programs available to the client 102. The application delivery system 190 receives a request to execute an enumerated application. The application delivery system 190 selects one of a predetermined number of methods for executing the enumerated application, for example, responsive to a policy of a policy engine. The application delivery system 190 may select a method of execution of the application enabling the client 102 to receive application-output data generated by execution of the application program on a server 106. The application delivery system 190 may select a method of execution of the application enabling the local machine 10 to execute the application program locally after retrieving a plurality of application files comprising the application. In yet another embodiment, the application delivery system 190 may select a method of execution of the application to stream the application via the network 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application, which can be any type and/or form of software, program, or executable instructions such as any type and/or form of web browser, web-based client, client-server application, a thin-client computing client, an ActiveX control, or a Java applet, or any other type and/or form of executable instructions capable of executing on client 102. In some embodiments, the application may be a server-based or a remote-based application executed on behalf of the client 102 on a server 106. In one embodiments the server 106 may display output to the client 102 using any thin-client or remote-display protocol, such as the Independent Computing Architecture (ICA) protocol manufactured by Citrix Systems, Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP) manufactured by the Microsoft Corporation of Redmond, Wash. The application can use any type of protocol and it can be, for example, an HTTP client, an FTP client, an Oscar client, or a Telnet client. In other embodiments, the application comprises any type of software related to VoIP communications, such as a soft IP telephone. In further embodiments, the application comprises any application related to real-time data communications, such as applications for streaming video and/or audio.

In some embodiments, the server 106 or a server farm 38 may be running one or more applications, such as an application providing a thin-client computing or remote display presentation application. In one embodiment, the server 106 or server farm 38 executes as an application, any portion of the Citrix Access Suite™ by Citrix Systems, Inc., such as the MetaFrame or Citrix Presentation Server™, and/or any of the Microsoft® Windows Terminal Services manufactured by the Microsoft Corporation. In one embodiment, the application is an ICA client, developed by Citrix Systems, Inc. of Fort Lauderdale, Fla. In other embodiments, the application includes a Remote Desktop (RDP) client, developed by Microsoft Corporation of Redmond, Wash. Also, the server 106 may run an application, which for example, may be an application server providing email services such as Microsoft Exchange manufactured by the Microsoft Corporation of Redmond, Wash., a web or Internet server, or a desktop sharing server, or a collaboration server. In some embodiments, any of the applications may comprise any type of hosted service or products, such as GoToMeeting™ provided by Citrix Online Division, Inc. of Santa Barbara, Calif., WebEx™ provided by WebEx, Inc. of Santa Clara, Calif., or Microsoft Office Live Meeting provided by Microsoft Corporation of Redmond, Wash.

Still referring to FIG. 1D, an embodiment of the network environment may include a monitoring server 106A. The monitoring server 106A may include any type and form performance monitoring service 198. The performance monitoring service 198 may include monitoring, measurement and/or management software and/or hardware, including data collection, aggregation, analysis, management and reporting. In one embodiment, the performance monitoring service 198 includes one or more monitoring agents 197. The monitoring agent 197 includes any software, hardware or combination thereof for performing monitoring, measurement and data collection activities on a device, such as a client 102, server 106 or an appliance 200, 205. In some embodiments, the monitoring agent 197 includes any type and form of script, such as Visual Basic script, or Javascript. In one embodiment, the monitoring agent 197 executes transparently to any application and/or user of the device. In some embodiments, the monitoring agent 197 is installed and operated unobtrusively to the application or client. In yet another embodiment, the monitoring agent 197 is installed and operated without any instrumentation for the application or device.

In some embodiments, the monitoring agent 197 monitors, measures and collects data on a predetermined frequency. In other embodiments, the monitoring agent 197 monitors, measures and collects data based upon detection of any type and form of event. For example, the monitoring agent 197 may collect data upon detection of a request for a web page or receipt of an HTTP response. In another example, the monitoring agent 197 may collect data upon detection of any user input events, such as a mouse click. The monitoring agent 197 may report or provide any monitored, measured or collected data to the monitoring service 198. In one embodiment, the monitoring agent 197 transmits information to the monitoring service 198 according to a schedule or a predetermined frequency. In another embodiment, the monitoring agent 197 transmits information to the monitoring service 198 upon detection of an event.

In some embodiments, the monitoring service 198 and/or monitoring agent 197 performs monitoring and performance measurement of any network resource or network infrastructure element, such as a client, server, server farm, appliance 200, appliance 205, or network connection. In one embodiment, the monitoring service 198 and/or monitoring agent 197 performs monitoring and performance measurement of any transport layer connection, such as a TCP or UDP connection. In another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures network latency. In yet one embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures bandwidth utilization.

In other embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures end-user response times. In some embodiments, the monitoring service 198 performs monitoring and performance measurement of an application. In another embodiment, the monitoring service 198 and/or monitoring agent 197 performs monitoring and performance measurement of any session or connection to the application. In one embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of a browser. In another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of HTTP based transactions. In some embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of a Voice over IP (VoIP) application or session. In other embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of a remote display protocol application, such as an ICA client or RDP client. In yet another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of any type and form of streaming media. In still a further embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of a hosted application or a Software-As-A-Service (SaaS) delivery model.

In some embodiments, the monitoring service 198 and/or monitoring agent 197 performs monitoring and performance measurement of one or more transactions, requests or responses related to application. In other embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures any portion of an application layer stack, such as any .NET or J2EE calls. In one embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures database or SQL transactions. In yet another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures any method, function or application programming interface (API) call.

In one embodiment, the monitoring service 198 and/or monitoring agent 197 performs monitoring and performance measurement of a delivery of application and/or data from a server to a client via one or more appliances, such as appliance 200 and/or appliance 205. In some embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of delivery of a virtualized application. In other embodiments, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of delivery of a streaming application. In another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of delivery of a desktop application to a client and/or the execution of the desktop application on the client. In another embodiment, the monitoring service 198 and/or monitoring agent 197 monitors and measures performance of a client/server application.

In one embodiment, the monitoring service 198 and/or monitoring agent 197 is designed and constructed to provide application performance management for the application delivery system 190. For example, the monitoring service 198 and/or monitoring agent 197 may monitor, measure and manage the performance of the delivery of applications via the Citrix Presentation Server. In this example, the monitoring service 198 and/or monitoring agent 197 monitors individual ICA sessions. The monitoring service 198 and/or monitoring agent 197 may measure the total and per session system resource usage, as well as application and networking performance. The monitoring service 198 and/or monitoring agent 197 may identify the active servers for a given user and/or user session. In some embodiments, the monitoring service 198 and/or monitoring agent 197 monitors back-end connections between the application delivery system 190 and an application and/or database server. The monitoring service 198 and/or monitoring agent 197 may measure network latency, delay and volume per user-session or ICA session.

In some embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors memory usage for the application delivery system 190, such as total memory usage, per user session and/or per process. In other embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors CPU usage the application delivery system 190, such as total CPU usage, per user session and/or per process. In another embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors the time required to log-in to an application, a server, or the application delivery system, such as Citrix Presentation Server. In one embodiment, the monitoring service 198 and/or monitoring agent 197 measures and monitors the duration a user is logged into an application, a server, or the application delivery system 190. In some embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors active and inactive session counts for an application, server or application delivery system session. In yet another embodiment, the monitoring service 198 and/or monitoring agent 197 measures and monitors user session latency.

In yet further embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors measures and monitors any type and form of server metrics. In one embodiment, the monitoring service 198 and/or monitoring agent 197 measures and monitors metrics related to system memory, CPU usage, and disk storage. In another embodiment, the monitoring service 198 and/or monitoring agent 197 measures and monitors metrics related to page faults, such as page faults per second. In other embodiments, the monitoring service 198 and/or monitoring agent 197 measures and monitors round-trip time metrics. In yet another embodiment, the monitoring service 198 and/or monitoring agent 197 measures and monitors metrics related to application crashes, errors and/or hangs.

In some embodiments, the monitoring service 198 and monitoring agent 198 includes any of the product embodiments referred to as EdgeSight manufactured by Citrix Systems, Inc. of Ft. Lauderdale, Fla. In another embodiment, the performance monitoring service 198 and/or monitoring agent 198 includes any portion of the product embodiments referred to as the TrueView product suite manufactured by the Symphoniq Corporation of Palo Alto, Calif. In one embodiment, the performance monitoring service 198 and/or monitoring agent 198 includes any portion of the product embodiments referred to as the TeaLeaf CX product suite manufactured by the TeaLeaf Technology Inc. of San Francisco, Calif. In other embodiments, the performance monitoring service 198 and/or monitoring agent 198 includes any portion of the business service management products, such as the BMC Performance Manager and Patrol products, manufactured by BMC Software, Inc. of Houston, Tex.

The client 102, server 106, and appliance 200 may be deployed as and/or executed on any type and form of computing device, such as a computer, network device or appliance capable of communicating on any type and form of network and performing the operations described herein. FIGS. 1E and 1F depict block diagrams of a computing device 100 useful for practicing an embodiment of the client 102, server 106 or appliance 200. As shown in FIGS. 1E and 1F, each computing device 100 includes a central processing unit 101, and a main memory unit 122. As shown in FIG. 1E, a computing device 100 may include a visual display device 124, a keyboard 126 and/or a pointing device 127, such as a mouse. Each computing device 100 may also include additional optional elements, such as one or more input/output devices 130 a-130 b (generally referred to using reference numeral 130), and a cache memory 140 in communication with the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds to and processes instructions fetched from the main memory unit 122. In many embodiments, the central processing unit is provided by a microprocessor unit, such as: those manufactured by Intel Corporation of Mountain View, Calif.; those manufactured by Motorola Corporation of Schaumburg, Illinois; those manufactured by Transmeta Corporation of Santa Clara, Calif.; the RS/6000 processor, those manufactured by International Business Machines of White Plains, New York; or those manufactured by Advanced Micro Devices of Sunnyvale, Calif. The computing device 100 may be based on any of these processors, or any other processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storing data and allowing any storage location to be directly accessed by the microprocessor 101, such as Static random access memory (SRAM), Burst SRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM), Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended Data Output RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), Burst Extended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM), synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data Rate SDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM), Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The main memory 122 may be based on any of the above described memory chips, or any other available memory chips capable of operating as described herein. In the embodiment shown in FIG. 1E, the processor 101 communicates with main memory 122 via a system bus 150 (described in more detail below). FIG. 1E depicts an embodiment of a computing device 100 in which the processor communicates directly with main memory 122 via a memory port 103. For example, in FIG. 1F the main memory 122 may be DRDRAM.

FIG. 1F depicts an embodiment in which the main processor 101 communicates directly with cache memory 140 via a secondary bus, sometimes referred to as a backside bus. In other embodiments, the main processor 101 communicates with cache memory 140 using the system bus 150. Cache memory 140 typically has a faster response time than main memory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In the embodiment shown in FIG. 1E, the processor 101 communicates with various I/O devices 130 via a local system bus 150. Various busses may be used to connect the central processing unit 101 to any of the I/O devices 130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannel Architecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or a NuBus. For embodiments in which the I/O device is a video display 124, the processor 101 may use an Advanced Graphics Port (AGP) to communicate with the display 124. FIG. 1F depicts an embodiment of a computer 100 in which the main processor 101 communicates directly with I/O device 130 via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1F also depicts an embodiment in which local busses and direct communication are mixed: the processor 101 communicates with I/O device 130 using a local interconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device 116, such as a floppy disk drive for receiving floppy disks such as 3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive, a DVD-ROM drive, tape drives of various formats, USB device, hard-drive or any other device suitable for installing software and programs such as any client agent 120, or portion thereof. The computing device 100 may further comprise a storage device 128, such as one or more hard disk drives or redundant arrays of independent disks, for storing an operating system and other related software, and for storing application software programs such as any program related to the client agent 120. Optionally, any of the installation devices 116 could also be used as the storage device 128. Additionally, the operating system and the software can be run from a bootable medium, for example, a bootable CD, such as KNOPPIX®, a bootable CD for GNU/Linux that is available as a GNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface 118 to interface to a Local Area Network (LAN), Wide Area Network (WAN) or the Internet through a variety of connections including, but not limited to, standard telephone lines, LAN or WAN links (e.g., 802.11, T1, T3, 56 kb, X.25), broadband connections (e.g., ISDN, Frame Relay, ATM), wireless connections, or some combination of any or all of the above. The network interface 118 may comprise a built-in network adapter, network interface card, PCMCIA network card, card bus network adapter, wireless network adapter, USB network adapter, modem or any other device suitable for interfacing the computing device 100 to any type of network capable of communication and performing the operations described herein.

A wide variety of I/O devices 130 a-130 n may be present in the computing device 100. Input devices include keyboards, mice, trackpads, trackballs, microphones, and drawing tablets. Output devices include video displays, speakers, inkjet printers, laser printers, and dye-sublimation printers. The I/O devices 130 may be controlled by an I/O controller 123 as shown in FIG. 1E. The I/O controller may control one or more I/O devices such as a keyboard 126 and a pointing device 127, e.g., a mouse or optical pen. Furthermore, an I/O device may also provide storage 128 and/or an installation medium 116 for the computing device 100. In still other embodiments, the computing device 100 may provide USB connections to receive handheld USB storage devices such as the USB Flash Drive line of devices manufactured by Twintech Industry, Inc. of Los Alamitos, California.

In some embodiments, the computing device 100 may comprise or be connected to multiple display devices 124 a-124 n, which each may be of the same or different type and/or form. As such, any of the I/O devices 130 a-130 n and/or the I/O controller 123 may comprise any type and/or form of suitable hardware, software, or combination of hardware and software to support, enable or provide for the connection and use of multiple display devices 124 a-124 n by the computing device 100. For example, the computing device 100 may include any type and/or form of video adapter, video card, driver, and/or library to interface, communicate, connect or otherwise use the display devices 124 a-124 n. In one embodiment, a video adapter may comprise multiple connectors to interface to multiple display devices 124 a-124 n. In other embodiments, the computing device 100 may include multiple video adapters, with each video adapter connected to one or more of the display devices 124 a-124 n. In some embodiments, any portion of the operating system of the computing device 100 may be configured for using multiple displays 124 a-124 n. In other embodiments, one or more of the display devices 124 a-124 n may be provided by one or more other computing devices, such as computing devices 100 a and 100 b connected to the computing device 100, for example, via a network. These embodiments may include any type of software designed and constructed to use another computer's display device as a second display device 124 a for the computing device 100. One ordinarily skilled in the art will recognize and appreciate the various ways and embodiments that a computing device 100 may be configured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 between the system bus 150 and an external communication bus, such as a USB bus, an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, a FireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, a Gigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, a Super HIPPI bus, a SerialPlus bus, a SCI/LAMP bus, a FibreChannel bus, or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1E and 1F typically operate under the control of operating systems, which control scheduling of tasks and access to system resources. The computing device 100 can be running any operating system such as any of the versions of the Microsoft® Windows operating systems, the different releases of the Unix and Linux operating systems, any version of the Mac OS® for Macintosh computers, any embedded operating system, any real-time operating system, any open source operating system, any proprietary operating system, any operating systems for mobile computing devices, or any other operating system capable of running on the computing device and performing the operations described herein. Typical operating systems include: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT 3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which are manufactured by Microsoft Corporation of Redmond, Wash.; MacOS, manufactured by Apple Computer of Cupertino, California; OS/2, manufactured by International Business Machines of Armonk, N.Y.; and Linux, a freely-available operating system distributed by Caldera Corp. of Salt Lake City, Utah, or any type and/or form of a Unix operating system, among others.

In other embodiments, the computing device 100 may have different processors, operating systems, and input devices consistent with the device. For example, in one embodiment the computer 100 is a Treo 180, 270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In this embodiment, the Treo smart phone is operated under the control of the PalmOS operating system and includes a stylus input device as well as a five-way navigator device. Moreover, the computing device 100 can be any workstation, desktop computer, laptop or notebook computer, server, handheld computer, mobile telephone, any other computer, or other form of computing or telecommunications device that is capable of communication and that has sufficient processor power and memory capacity to perform the operations described herein.

B. Appliance Architecture

FIG. 2A illustrates an example embodiment of the appliance 200. The architecture of the appliance 200 in FIG. 2A is provided by way of illustration only and is not intended to be limiting. As shown in FIG. 2, appliance 200 comprises a hardware layer 206 and a software layer divided into a user space 202 and a kernel space 204.

Hardware layer 206 provides the hardware elements upon which programs and services within kernel space 204 and user space 202 are executed. Hardware layer 206 also provides the structures and elements which allow programs and services within kernel space 204 and user space 202 to communicate data both internally and externally with respect to appliance 200. As shown in FIG. 2, the hardware layer 206 includes a processing unit 262 for executing software programs and services, a memory 264 for storing software and data, network ports 266 for transmitting and receiving data over a network, and an encryption processor 260 for performing functions related to Secure Sockets Layer processing of data transmitted and received over the network. In some embodiments, the central processing unit 262 may perform the functions of the encryption processor 260 in a single processor. Additionally, the hardware layer 206 may comprise multiple processors for each of the processing unit 262 and the encryption processor 260. The processor 262 may include any of the processors 101 described above in connection with FIGS. 1E and 1F. In some embodiments, the central processing unit 262 may perform the functions of the encryption processor 260 in a single processor. Additionally, the hardware layer 206 may comprise multiple processors for each of the processing unit 262 and the encryption processor 260. For example, in one embodiment, the appliance 200 comprises a first processor 262 and a second processor 262′. In other embodiments, the processor 262 or 262′ comprises a multi-core processor.

Although the hardware layer 206 of appliance 200 is generally illustrated with an encryption processor 260, processor 260 may be a processor for performing functions related to any encryption protocol, such as the Secure Socket Layer (SSL) or Transport Layer Security (TLS) protocol. In some embodiments, the processor 260 may be a general purpose processor (GPP), and in further embodiments, may be have executable instructions for performing processing of any security related protocol.

Although the hardware layer 206 of appliance 200 is illustrated with certain elements in FIG. 2, the hardware portions or components of appliance 200 may comprise any type and form of elements, hardware or software, of a computing device, such as the computing device 100 illustrated and discussed herein in conjunction with FIGS. 1E and 1F. In some embodiments, the appliance 200 may comprise a server, gateway, router, switch, bridge or other type of computing or network device, and have any hardware and/or software elements associated therewith.

The operating system of appliance 200 allocates, manages, or otherwise segregates the available system memory into kernel space 204 and user space 204. In example software architecture 200, the operating system may be any type and/or form of Unix operating system although the invention is not so limited. As such, the appliance 200 can be running any operating system such as any of the versions of the Microsoft® Windows operating systems, the different releases of the Unix and Linux operating systems, any version of the Mac OS® for Macintosh computers, any embedded operating system, any network operating system, any real-time operating system, any open source operating system, any proprietary operating system, any operating systems for mobile computing devices or network devices, or any other operating system capable of running on the appliance 200 and performing the operations described herein.

The kernel space 204 is reserved for running the kernel 230, including any device drivers, kernel extensions or other kernel related software. As known to those skilled in the art, the kernel 230 is the core of the operating system, and provides access, control, and management of resources and hardware-related elements of the application 104. In accordance with an embodiment of the appliance 200, the kernel space 204 also includes a number of network services or processes working in conjunction with a cache manager 232, sometimes also referred to as the integrated cache, the benefits of which are described in detail further herein. Additionally, the embodiment of the kernel 230 will depend on the embodiment of the operating system installed, configured, or otherwise used by the device 200.

In one embodiment, the device 200 comprises one network stack 267, such as a TCP/IP based stack, for communicating with the client 102 and/or the server 106. In one embodiment, the network stack 267 is used to communicate with a first network, such as network 108, and a second network 110. In some embodiments, the device 200 terminates a first transport layer connection, such as a TCP connection of a client 102, and establishes a second transport layer connection to a server 106 for use by the client 102, e.g., the second transport layer connection is terminated at the appliance 200 and the server 106. The first and second transport layer connections may be established via a single network stack 267. In other embodiments, the device 200 may comprise multiple network stacks, for example 267 and 267′, and the first transport layer connection may be established or terminated at one network stack 267, and the second transport layer connection on the second network stack 267′. For example, one network stack may be for receiving and transmitting network packet on a first network, and another network stack for receiving and transmitting network packets on a second network. In one embodiment, the network stack 267 comprises a buffer 243 for queuing one or more network packets for transmission by the appliance 200.

As shown in FIG. 2, the kernel space 204 includes the cache manager 232, a high-speed layer 2-7 integrated packet engine 240, an encryption engine 234, a policy engine 236 and multi-protocol compression logic 238. Running these components or processes 232, 240, 234, 236 and 238 in kernel space 204 or kernel mode instead of the user space 202 improves the performance of each of these components, alone and in combination. Kernel operation means that these components or processes 232, 240, 234, 236 and 238 run in the core address space of the operating system of the device 200. For example, running the encryption engine 234 in kernel mode improves encryption performance by moving encryption and decryption operations to the kernel, thereby reducing the number of transitions between the memory space or a kernel thread in kernel mode and the memory space or a thread in user mode. For example, data obtained in kernel mode may not need to be passed or copied to a process or thread running in user mode, such as from a kernel level data structure to a user level data structure. In another aspect, the number of context switches between kernel mode and user mode are also reduced. Additionally, synchronization of and communications between any of the components or processes 232, 240, 235, 236 and 238 can be performed more efficiently in the kernel space 204.

In some embodiments, any portion of the components 232, 240, 234, 236 and 238 may run or operate in the kernel space 204, while other portions of these components 232, 240, 234, 236 and 238 may run or operate in user space 202. In one embodiment, the appliance 200 uses a kernel-level data structure providing access to any portion of one or more network packets, for example, a network packet comprising a request from a client 102 or a response from a server 106. In some embodiments, the kernel-level data structure may be obtained by the packet engine 240 via a transport layer driver interface or filter to the network stack 267. The kernel-level data structure may comprise any interface and/or data accessible via the kernel space 204 related to the network stack 267, network traffic or packets received or transmitted by the network stack 267. In other embodiments, the kernel-level data structure may be used by any of the components or processes 232, 240, 234, 236 and 238 to perform the desired operation of the component or process. In one embodiment, a component 232, 240, 234, 236 and 238 is running in kernel mode 204 when using the kernel-level data structure, while in another embodiment, the component 232, 240, 234, 236 and 238 is running in user mode when using the kernel-level data structure. In some embodiments, the kernel-level data structure may be copied or passed to a second kernel-level data structure, or any desired user-level data structure.

The cache manager 232 may comprise software, hardware or any combination of software and hardware to provide cache access, control and management of any type and form of content, such as objects or dynamically generated objects served by the originating servers 106. The data, objects or content processed and stored by the cache manager 232 may comprise data in any format, such as a markup language, or communicated via any protocol. In some embodiments, the cache manager 232 duplicates original data stored elsewhere or data previously computed, generated or transmitted, in which the original data may require longer access time to fetch, compute or otherwise obtain relative to reading a cache memory element. Once the data is stored in the cache memory element, future use can be made by accessing the cached copy rather than refetching or recomputing the original data, thereby reducing the access time. In some embodiments, the cache memory element may comprise a data object in memory 264 of device 200. In other embodiments, the cache memory element may comprise memory having a faster access time than memory 264. In another embodiment, the cache memory element may comprise any type and form of storage element of the device 200, such as a portion of a hard disk. In some embodiments, the processing unit 262 may provide cache memory for use by the cache manager 232. In yet further embodiments, the cache manager 232 may use any portion and combination of memory, storage, or the processing unit for caching data, objects, and other content.

Furthermore, the cache manager 232 includes any logic, functions, rules, or operations to perform any embodiments of the techniques of the appliance 200 described herein. For example, the cache manager 232 includes logic or functionality to invalidate objects based on the expiration of an invalidation time period or upon receipt of an invalidation command from a client 102 or server 106. In some embodiments, the cache manager 232 may operate as a program, service, process or task executing in the kernel space 204, and in other embodiments, in the user space 202. In one embodiment, a first portion of the cache manager 232 executes in the user space 202 while a second portion executes in the kernel space 204. In some embodiments, the cache manager 232 can comprise any type of general purpose processor (GPP), or any other type of integrated circuit, such as a Field Programmable Gate Array (FPGA), Programmable Logic Device (PLD), or Application Specific Integrated Circuit (ASIC).

The policy engine 236 may include, for example, an intelligent statistical engine or other programmable application(s). In one embodiment, the policy engine 236 provides a configuration mechanism to allow a user to identify, specify, define or configure a caching policy. Policy engine 236, in some embodiments, also has access to memory to support data structures such as lookup tables or hash tables to enable user-selected caching policy decisions. In other embodiments, the policy engine 236 may comprise any logic, rules, functions or operations to determine and provide access, control and management of objects, data or content being cached by the appliance 200 in addition to access, control and management of security, network traffic, network access, compression or any other function or operation performed by the appliance 200. Further examples of specific caching policies are further described herein.

In some embodiments, the policy engine 236 may provide a configuration mechanism to allow a user to identify, specify, define or configure policies directing behavior of any other components or functionality of an appliance, including without limitation the components described in FIG. 2B such as vServers 275, VPN functions 280, Intranet IP functions 282, switching functions 284, DNS functions 286, acceleration functions 288, application firewall functions 290, and monitoring agents 197. In other embodiments, the policy engine 236 may check, evaluate, implement, or otherwise act in response to any configured policies, and may also direct the operation of one or more appliance functions in response to a policy.

The encryption engine 234 comprises any logic, business rules, functions or operations for handling the processing of any security related protocol, such as SSL or TLS, or any function related thereto. For example, the encryption engine 234 encrypts and decrypts network packets, or any portion thereof, communicated via the appliance 200. The encryption engine 234 may also setup or establish SSL or TLS connections on behalf of the client 102 a-102 n, server 106 a-106 n, or appliance 200. As such, the encryption engine 234 provides offloading and acceleration of SSL processing. In one embodiment, the encryption engine 234 uses a tunneling protocol to provide a virtual private network between a client 102 a-102 n and a server 106 a-106 n. In some embodiments, the encryption engine 234 is in communication with the Encryption processor 260. In other embodiments, the encryption engine 234 comprises executable instructions running on the Encryption processor 260.

The multi-protocol compression engine 238 comprises any logic, business rules, function or operations for compressing one or more protocols of a network packet, such as any of the protocols used by the network stack 267 of the device 200. In one embodiment, multi-protocol compression engine 238 compresses bi-directionally between clients 102 a-102 n and servers 106 a-106 n any TCP/IP based protocol, including Messaging Application Programming Interface (MAPI) (email), File Transfer Protocol (FTP), HyperText Transfer Protocol (HTTP), Common Internet File System (CIFS) protocol (file transfer), Independent Computing Architecture (ICA) protocol, Remote Desktop Protocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol. In other embodiments, multi-protocol compression engine 238 provides compression of Hypertext Markup Language (HTML) based protocols and in some embodiments, provides compression of any markup languages, such as the Extensible Markup Language (XML). In one embodiment, the multi-protocol compression engine 238 provides compression of any high-performance protocol, such as any protocol designed for appliance 200 to appliance 200 communications. In another embodiment, the multi-protocol compression engine 238 compresses any payload of or any communication using a modified transport control protocol, such as Transaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP with large windows (TCP-LW), a congestion prediction protocol such as the TCP-Vegas protocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 accelerates performance for users accessing applications via desktop clients, e.g., Microsoft Outlook and non-Web thin clients, such as any client launched by popular enterprise applications like Oracle, SAP and Siebel, and even mobile clients, such as the Pocket PC. In some embodiments, the multi-protocol compression engine 238 by executing in the kernel mode 204 and integrating with packet processing engine 240 accessing the network stack 267 is able to compress any of the protocols carried by the TCP/IP protocol, such as any application layer protocol.

High speed layer 2-7 integrated packet engine 240, also generally referred to as a packet processing engine or packet engine, is responsible for managing the kernel-level processing of packets received and transmitted by appliance 200 via network ports 266. The high speed layer 2-7 integrated packet engine 240 may comprise a buffer for queuing one or more network packets during processing, such as for receipt of a network packet or transmission of a network packer. Additionally, the high speed layer 2-7 integrated packet engine 240 is in communication with one or more network stacks 267 to send and receive network packets via network ports 266. The high speed layer 2-7 integrated packet engine 240 works in conjunction with encryption engine 234, cache manager 232, policy engine 236 and multi-protocol compression logic 238. In particular, encryption engine 234 is configured to perform SSL processing of packets, policy engine 236 is configured to perform functions related to traffic management such as request-level content switching and request-level cache redirection, and multi-protocol compression logic 238 is configured to perform functions related to compression and decompression of data.

The high speed layer 2-7 integrated packet engine 240 includes a packet processing timer 242. In one embodiment, the packet processing timer 242 provides one or more time intervals to trigger the processing of incoming, i.e., received, or outgoing, i.e., transmitted, network packets. In some embodiments, the high speed layer 2-7 integrated packet engine 240 processes network packets responsive to the timer 242. The packet processing timer 242 provides any type and form of signal to the packet engine 240 to notify, trigger, or communicate a time related event, interval or occurrence. In many embodiments, the packet processing timer 242 operates in the order of milliseconds, such as for example 100 ms, 50 ms or 25 ms. For example, in some embodiments, the packet processing timer 242 provides time intervals or otherwise causes a network packet to be processed by the high speed layer 2-7 integrated packet engine 240 at a 10 ms time interval, while in other embodiments, at a 5 ms time interval, and still yet in further embodiments, as short as a 3, 2, or 1 ms time interval. The high speed layer 2-7 integrated packet engine 240 may be interfaced, integrated or in communication with the encryption engine 234, cache manager 232, policy engine 236 and multi-protocol compression engine 238 during operation. As such, any of the logic, functions, or operations of the encryption engine 234, cache manager 232, policy engine 236 and multi-protocol compression logic 238 may be performed responsive to the packet processing timer 242 and/or the packet engine 240. Therefore, any of the logic, functions, or operations of the encryption engine 234, cache manager 232, policy engine 236 and multi-protocol compression logic 238 may be performed at the granularity of time intervals provided via the packet processing timer 242, for example, at a time interval of less than or equal to 10 ms. For example, in one embodiment, the cache manager 232 may perform invalidation of any cached objects responsive to the high speed layer 2-7 integrated packet engine 240 and/or the packet processing timer 242. In another embodiment, the expiry or invalidation time of a cached object can be set to the same order of granularity as the time interval of the packet processing timer 242, such as at every 10 ms.

In contrast to kernel space 204, user space 202 is the memory area or portion of the operating system used by user mode applications or programs otherwise running in user mode. A user mode application may not access kernel space 204 directly and uses service calls in order to access kernel services. As shown in FIG. 2, user space 202 of appliance 200 includes a graphical user interface (GUI) 210, a command line interface (CLI) 212, shell services 214, health monitoring program 216, and daemon services 218. GUI 210 and CLI 212 provide a means by which a system administrator or other user can interact with and control the operation of appliance 200, such as via the operating system of the appliance 200 and either is user space 202 or kernel space 204. The GUI 210 may be any type and form of graphical user interface and may be presented via text, graphical or otherwise, by any type of program or application, such as a browser. The CLI 212 may be any type and form of command line or text-based interface, such as a command line provided by the operating system. For example, the CLI 212 may comprise a shell, which is a tool to enable users to interact with the operating system. In some embodiments, the CLI 212 may be provided via a bash, csh, tcsh, or ksh type shell. The shell services 214 comprises the programs, services, tasks, processes or executable instructions to support interaction with the appliance 200 or operating system by a user via the GUI 210 and/or CLI 212.

Health monitoring program 216 is used to monitor, check, report and ensure that network systems are functioning properly and that users are receiving requested content over a network. Health monitoring program 216 comprises one or more programs, services, tasks, processes or executable instructions to provide logic, rules, functions or operations for monitoring any activity of the appliance 200. In some embodiments, the health monitoring program 216 intercepts and inspects any network traffic passed via the appliance 200. In other embodiments, the health monitoring program 216 interfaces by any suitable means and/or mechanisms with one or more of the following: the encryption engine 234, cache manager 232, policy engine 236, multi-protocol compression logic 238, packet engine 240, daemon services 218, and shell services 214. As such, the health monitoring program 216 may call any application programming interface (API) to determine a state, status, or health of any portion of the appliance 200. For example, the health monitoring program 216 may ping or send a status inquiry on a periodic basis to check if a program, process, service or task is active and currently running. In another example, the health monitoring program 216 may check any status, error or history logs provided by any program, process, service or task to determine any condition, status or error with any portion of the appliance 200.

Daemon services 218 are programs that run continuously or in the background and handle periodic service requests received by appliance 200. In some embodiments, a daemon service may forward the requests to other programs or processes, such as another daemon service 218 as appropriate. As known to those skilled in the art, a daemon service 218 may run unattended to perform continuous or periodic system wide functions, such as network control, or to perform any desired task. In some embodiments, one or more daemon services 218 run in the user space 202, while in other embodiments, one or more daemon services 218 run in the kernel space.

Referring now to FIG. 2B, another embodiment of the appliance 200 is depicted. In brief overview, the appliance 200 provides one or more of the following services, functionality or operations: SSL VPN connectivity 280, switching/load balancing 284, Domain Name Service resolution 286, acceleration 288 and an application firewall 290 for communications between one or more clients 102 and one or more servers 106. Each of the servers 106 may provide one or more network related services 270 a-270 n (referred to as services 270). For example, a server 106 may provide an http service 270. The appliance 200 comprises one or more virtual servers or virtual internet protocol servers, referred to as a vServer, VIP server, or just VIP 275 a-275 n (also referred herein as vServer 275). The vServer 275 receives, intercepts or otherwise processes communications between a client 102 and a server 106 in accordance with the configuration and operations of the appliance 200.

The vServer 275 may comprise software, hardware or any combination of software and hardware. The vServer 275 may comprise any type and form of program, service, task, process or executable instructions operating in user mode 202, kernel mode 204 or any combination thereof in the appliance 200. The vServer 275 includes any logic, functions, rules, or operations to perform any embodiments of the techniques described herein, such as SSL VPN 280, switching/load balancing 284, Domain Name Service resolution 286, acceleration 288 and an application firewall 290. In some embodiments, the vServer 275 establishes a connection to a service 270 of a server 106. The service 275 may comprise any program, application, process, task or set of executable instructions capable of connecting to and communicating to the appliance 200, client 102 or vServer 275. For example, the service 275 may comprise a web server, http server, ftp, email or database server. In some embodiments, the service 270 is a daemon process or network driver for listening, receiving and/or sending communications for an application, such as email, database or an enterprise application. In some embodiments, the service 270 may communicate on a specific IP address, or IP address and port.

In some embodiments, the vServer 275 applies one or more policies of the policy engine 236 to network communications between the client 102 and server 106. In one embodiment, the policies are associated with a VServer 275. In another embodiment, the policies are based on a user, or a group of users. In yet another embodiment, a policy is global and applies to one or more vServers 275 a-275 n, and any user or group of users communicating via the appliance 200. In some embodiments, the policies of the policy engine have conditions upon which the policy is applied based on any content of the communication, such as internet protocol address, port, protocol type, header or fields in a packet, or the context of the communication, such as user, group of the user, vServer 275, transport layer connection, and/or identification or attributes of the client 102 or server 106.

In other embodiments, the appliance 200 communicates or interfaces with the policy engine 236 to determine authentication and/or authorization of a remote user or a remote client 102 to access the computing environment 15, application, and/or data file from a server 106. In another embodiment, the appliance 200 communicates or interfaces with the policy engine 236 to determine authentication and/or authorization of a remote user or a remote client 102 to have the application delivery system 190 deliver one or more of the computing environment 15, application, and/or data file. In yet another embodiment, the appliance 200 establishes a VPN or SSL VPN connection based on the policy engine's 236 authentication and/or authorization of a remote user or a remote client 103 In one embodiment, the appliance 102 controls the flow of network traffic and communication sessions based on policies of the policy engine 236. For example, the appliance 200 may control the access to a computing environment 15, application or data file based on the policy engine 236.

In some embodiments, the vServer 275 establishes a transport layer connection, such as a TCP or UDP connection with a client 102 via the client agent 120. In one embodiment, the vServer 275 listens for and receives communications from the client 102. In other embodiments, the vServer 275 establishes a transport layer connection, such as a TCP or UDP connection with a client server 106. In one embodiment, the vServer 275 establishes the transport layer connection to an internet protocol address and port of a server 270 running on the server 106. In another embodiment, the vServer 275 associates a first transport layer connection to a client 102 with a second transport layer connection to the server 106. In some embodiments, a vServer 275 establishes a pool of transport layer connections to a server 106 and multiplexes client requests via the pooled transport layer connections.

In some embodiments, the appliance 200 provides a SSL VPN connection 280 between a client 102 and a server 106. For example, a client 102 on a first network 102 requests to establish a connection to a server 106 on a second network 104′. In some embodiments, the second network 104′ is not routable from the first network 104. In other embodiments, the client 102 is on a public network 104 and the server 106 is on a private network 104′, such as a corporate network. In one embodiment, the client agent 120 intercepts communications of the client 102 on the first network 104, encrypts the communications, and transmits the communications via a first transport layer connection to the appliance 200. The appliance 200 associates the first transport layer connection on the first network 104 to a second transport layer connection to the server 106 on the second network 104. The appliance 200 receives the intercepted communication from the client agent 102, decrypts the communications, and transmits the communication to the server 106 on the second network 104 via the second transport layer connection. The second transport layer connection may be a pooled transport layer connection. As such, the appliance 200 provides an end-to-end secure transport layer connection for the client 102 between the two networks 104, 104′.

In one embodiment, the appliance 200 hosts an intranet internet protocol or intranetIP 282 address of the client 102 on the virtual private network 104. The client 102 has a local network identifier, such as an internet protocol (IP) address and/or host name on the first network 104. When connected to the second network 104′ via the appliance 200, the appliance 200 establishes, assigns or otherwise provides an IntranetIP, which is network identifier, such as IP address and/or host name, for the client 102 on the second network 104′. The appliance 200 listens for and receives on the second or private network 104′ for any communications directed towards the client 102 using the client's established IntranetIP 282. In one embodiment, the appliance 200 acts as or on behalf of the client 102 on the second private network 104. For example, in another embodiment, a vServer 275 listens for and responds to communications to the IntranetIP 282 of the client 102. In some embodiments, if a computing device 100 on the second network 104′ transmits a request, the appliance 200 processes the request as if it were the client 102. For example, the appliance 200 may respond to a ping to the client's IntranetIP 282. In another example, the appliance may establish a connection, such as a TCP or UDP connection, with computing device 100 on the second network 104 requesting a connection with the client's IntranetIP 282.

In some embodiments, the appliance 200 provides one or more of the following acceleration techniques 288 to communications between the client 102 and server 106: 1) compression; 2) decompression; 3) Transmission Control Protocol pooling; 4) Transmission Control Protocol multiplexing; 5) Transmission Control Protocol buffering; and 6) caching.

In one embodiment, the appliance 200 relieves servers 106 of much of the processing load caused by repeatedly opening and closing transport layers connections to clients 102 by opening one or more transport layer connections with each server 106 and maintaining these connections to allow repeated data accesses by clients via the Internet. This technique is referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from a client 102 to a server 106 via a pooled transport layer connection, the appliance 200 translates or multiplexes communications by modifying sequence number and acknowledgment numbers at the transport layer protocol level. This is referred to as “connection multiplexing”. In some embodiments, no application layer protocol interaction is required. For example, in the case of an in-bound packet (that is, a packet received from a client 102), the source network address of the packet is changed to that of an output port of appliance 200, and the destination network address is changed to that of the intended server. In the case of an outbound packet (that is, one received from a server 106), the source network address is changed from that of the server 106 to that of an output port of appliance 200 and the destination address is changed from that of appliance 200 to that of the requesting client 102. The sequence numbers and acknowledgment numbers of the packet are also translated to sequence numbers and acknowledgement expected by the client 102 on the appliance's 200 transport layer connection to the client 102. In some embodiments, the packet checksum of the transport layer protocol is recalculated to account for these translations.

In another embodiment, the appliance 200 provides switching or load-balancing functionality 284 for communications between the client 102 and server 106. In some embodiments, the appliance 200 distributes traffic and directs client requests to a server 106 based on layer 4 or application-layer request data. In one embodiment, although the network layer or layer 2 of the network packet identifies a destination server 106, the appliance 200 determines the server 106 to distribute the network packet by application information and data carried as payload of the transport layer packet. In one embodiment, the health monitoring programs 216 of the appliance 200 monitor the health of servers to determine the server 106 for which to distribute a client's request. In some embodiments, if the appliance 200 detects a server 106 is not available or has a load over a predetermined threshold, the appliance 200 can direct or distribute client requests to another server 106.

In some embodiments, the appliance 200 acts as a Domain Name Service (DNS) resolver or otherwise provides resolution of a DNS request from clients 102. In some embodiments, the appliance intercepts' a DNS request transmitted by the client 102. In one embodiment, the appliance 200 responds to a client's DNS request with an IP address of or hosted by the appliance 200. In this embodiment, the client 102 transmits network communication for the domain name to the appliance 200. In another embodiment, the appliance 200 responds to a client's DNS request with an IP address of or hosted by a second appliance 200′. In some embodiments, the appliance 200 responds to a client's DNS request with an IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 200 provides application firewall functionality 290 for communications between the client 102 and server 106. In one embodiment, the policy engine 236 provides rules for detecting and blocking illegitimate requests. In some embodiments, the application firewall 290 protects against denial of service (DoS) attacks. In other embodiments, the appliance inspects the content of intercepted requests to identify and block application-based attacks. In some embodiments, the rules/policy engine 236 comprises one or more application firewall or security control policies for providing protections against various classes and types of web or Internet based vulnerabilities, such as one or more of the following: 1) buffer overflow, 2) CGI-BIN parameter manipulation, 3) form/hidden field manipulation, 4) forceful browsing, 5) cookie or session poisoning, 6) broken access control list (ACLs) or weak passwords, 7) cross-site scripting (XSS), 8) command injection, 9) SQL injection, 10) error triggering sensitive information leak, 11) insecure use of cryptography, 12) server misconfiguration, 13) back doors and debug options, 14) website defacement, 15) platform or operating systems vulnerabilities, and 16) zero-day exploits. In an embodiment, the application firewall 290 provides HTML form field protection in the form of inspecting or analyzing the network communication for one or more of the following: 1) required fields are returned, 2) no added field allowed, 3) read-only and hidden field enforcement, 4) drop-down list and radio button field conformance, and 5) form-field max-length enforcement. In some embodiments, the application firewall 290 ensures cookies are not modified. In other embodiments, the application firewall 290 protects against forceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall 290 protects any confidential information contained in the network communication. The application firewall 290 may inspect or analyze any network communication in accordance with the rules or polices of the engine 236 to identify any confidential information in any field of the network packet. In some embodiments, the application firewall 290 identifies in the network communication one or more occurrences of a credit card number, password, social security number, name, patient code, contact information, and age. The encoded portion of the network communication may comprise these occurrences or the confidential information. Based on these occurrences, in one embodiment, the application firewall 290 may take a policy action on the network communication, such as prevent transmission of the network communication. In another embodiment, the application firewall 290 may rewrite, remove or otherwise mask such identified occurrence or confidential information.

Still referring to FIG. 2B, the appliance 200 may include a performance monitoring agent 197 as discussed above in conjunction with FIG. 1D. In one embodiment, the appliance 200 receives the monitoring agent 197 from the monitoring service 1908 or monitoring server 106 as depicted in FIG. 1D. In some embodiments, the appliance 200 stores the monitoring agent 197 in storage, such as disk, for delivery to any client or server in communication with the appliance 200. For example, in one embodiment, the appliance 200 transmits the monitoring agent 197 to a client upon receiving a request to establish a transport layer connection. In other embodiments, the appliance 200 transmits the monitoring agent 197 upon establishing the transport layer connection with the client 102. In another embodiment, the appliance 200 transmits the monitoring agent 197 to the client upon intercepting or detecting a request for a web page. In yet another embodiment, the appliance 200 transmits the monitoring agent 197 to a client or a server in response to a request from the monitoring server 198. In one embodiment, the appliance 200 transmits the monitoring agent 197 to a second appliance 200′ or appliance 205.

In other embodiments, the appliance 200 executes the monitoring agent 197. In one embodiment, the monitoring agent 197 measures and monitors the performance of any application, program, process, service, task or thread executing on the appliance 200. For example, the monitoring agent 197 may monitor and measure performance and operation of vServers 275A-275N. In another embodiment, the monitoring agent 197 measures and monitors the performance of any transport layer connections of the appliance 200. In some embodiments, the monitoring agent 197 measures and monitors the performance of any user sessions traversing the appliance 200. In one embodiment, the monitoring agent 197 measures and monitors the performance of any virtual private network connections and/or sessions traversing the appliance 200, such an SSL VPN session. In still further embodiments, the monitoring agent 197 measures and monitors the memory, CPU and disk usage and performance of the appliance 200. In yet another embodiment, the monitoring agent 197 measures and monitors the performance of any acceleration technique 288 performed by the appliance 200, such as SSL offloading, connection pooling and multiplexing, caching, and compression. In some embodiments, the monitoring agent 197 measures and monitors the performance of any load balancing and/or content switching 284 performed by the appliance 200. In other embodiments, the monitoring agent 197 measures and monitors the performance of application firewall 290 protection and processing performed by the appliance 200.

C. Client Agent

Referring now to FIG. 3, an embodiment of the client agent 120 is depicted. The client 102 includes a client agent 120 for establishing and exchanging communications with the appliance 200 and/or server 106 via a network 104. In brief overview, the client 102 operates on computing device 100 having an operating system with a kernel mode 302 and a user mode 303, and a network stack 310 with one or more layers 310 a-310 b. The client 102 may have installed and/or execute one or more applications. In some embodiments, one or more applications may communicate via the network stack 310 to a network 104. One of the applications, such as a web browser, may also include a first program 322. For example, the first program 322 may be used in some embodiments to install and/or execute the client agent 120, or any portion thereof. The client agent 120 includes an interception mechanism, or interceptor 350, for intercepting network communications from the network stack 310 from the one or more applications.

The network stack 310 of the client 102 may comprise any type and form of software, or hardware, or any combinations thereof, for providing connectivity to and communications with a network. In one embodiment, the network stack 310 comprises a software implementation for a network protocol suite. The network stack 310 may comprise one or more network layers, such as any networks layers of the Open Systems Interconnection (OSI) communications model as those skilled in the art recognize and appreciate. As such, the network stack 310 may comprise any type and form of protocols for any of the following layers of the OSI model: 1) physical link layer, 2) data link layer, 3) network layer, 4) transport layer, 5) session layer, 6) presentation layer, and 7) application layer. In one embodiment, the network stack 310 may comprise a transport control protocol (TCP) over the network layer protocol of the internet protocol (IP), generally referred to as TCP/IP. In some embodiments, the TCP/IP protocol may be carried over the Ethernet protocol, which may comprise any of the family of IEEE wide-area-network (WAN) or local-area-network (LAN) protocols, such as those protocols covered by the IEEE 802.3. In some embodiments, the network stack 310 comprises any type and form of a wireless protocol, such as IEEE 802.11 and/or mobile internet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may be used, including Messaging Application Programming Interface (MAPI) (email), File Transfer Protocol (FTP), HyperText Transfer Protocol (HTTP), Common Internet File System (CIFS) protocol (file transfer), Independent Computing Architecture (ICA) protocol, Remote Desktop Protocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol. In another embodiment, the network stack 310 comprises any type and form of transport control protocol, such as a modified transport control protocol, for example a Transaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP with large windows (TCP-LW), a congestion prediction protocol such as the TCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments, any type and form of user datagram protocol (UDP), such as UDP over IP, may be used by the network stack 310, such as for voice communications or real-time data communications.

Furthermore, the network stack 310 may include one or more network drivers supporting the one or more layers, such as a TCP driver or a network layer driver. The network drivers may be included as part of the operating system of the computing device 100 or as part of any network interface cards or other network access components of the computing device 100. In some embodiments, any of the network drivers of the network stack 310 may be customized, modified or adapted to provide a custom or modified portion of the network stack 310 in support of any of the techniques described herein. In other embodiments, the acceleration program 120 is designed and constructed to operate with or work in conjunction with the network stack 310 installed or otherwise provided by the operating system of the client 102.

The network stack 310 comprises any type and form of interfaces for receiving, obtaining, providing or otherwise accessing any information and data related to network communications of the client 102. In one embodiment, an interface to the network stack 310 comprises an application programming interface (API). The interface may also comprise any function call, hooking or filtering mechanism, event or call back mechanism, or any type of interfacing technique. The network stack 310 via the interface may receive or provide any type and form of data structure, such as an object, related to functionality or operation of the network stack 310. For example, the data structure may comprise information and data related to a network packet or one or more network packets. In some embodiments, the data structure comprises a portion of the network packet processed at a protocol layer of the network stack 310, such as a network packet of the transport layer. In some embodiments, the data structure 325 comprises a kernel-level data structure, while in other embodiments, the data structure 325 comprises a user-mode data structure. A kernel-level data structure may comprise a data structure obtained or related to a portion of the network stack 310 operating in kernel-mode 302, or a network driver or other software running in kernel-mode 302, or any data structure obtained or received by a service, process, task, thread or other executable instructions running or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 310 may execute or operate in kernel-mode 302, for example, the data link or network layer, while other portions execute or operate in user-mode 303, such as an application layer of the network stack 310. For example, a first portion 310 a of the network stack may provide user-mode access to the network stack 310 to an application while a second portion 310 a of the network stack 310 provides access to a network. In some embodiments, a first portion 310 a of the network stack may comprise one or more upper layers of the network stack 310, such as any of layers 5-7. In other embodiments, a second portion 310 b of the network stack 310 comprises one or more lower layers, such as any of layers 1-4. Each of the first portion 310 a and second portion 310 b of the network stack 310 may comprise any portion of the network stack 310, at any one or more network layers, in user-mode 203, kernel-mode, 202, or combinations thereof, or at any portion of a network layer or interface point to a network layer or any portion of or interface point to the user-mode 203 and kernel-mode 203.

The interceptor 350 may comprise software, hardware, or any combination of software and hardware. In one embodiment, the interceptor 350 intercept a network communication at any point in the network stack 310, and redirects or transmits the network communication to a destination desired, managed or controlled by the interceptor 350 or client agent 120. For example, the interceptor 350 may intercept a network communication of a network stack 310 of a first network and transmit the network communication to the appliance 200 for transmission on a second network 104. In some embodiments, the interceptor 350 comprises any type interceptor 350 comprises a driver, such as a network driver constructed and designed to interface and work with the network stack 310. In some embodiments, the client agent 120 and/or interceptor 350 operates at one or more layers of the network stack 310, such as at the transport layer. In one embodiment, the interceptor 350 comprises a filter driver, hooking mechanism, or any form and type of suitable network driver interface that interfaces to the transport layer of the network stack, such as via the transport driver interface (TDI). In some embodiments, the interceptor 350 interfaces to a first protocol layer, such as the transport layer and another protocol layer, such as any layer above the transport protocol layer, for example, an application protocol layer. In one embodiment, the interceptor 350 may comprise a driver complying with the Network Driver Interface Specification (NDIS), or a NDIS driver. In another embodiment, the interceptor 350 may comprise a min-filter or a mini-port driver. In one embodiment, the interceptor 350, or portion thereof, operates in kernel-mode 202. In another embodiment, the interceptor 350, or portion thereof, operates in user-mode 203. In some embodiments, a portion of the interceptor 350 operates in kernel-mode 202 while another portion of the interceptor 350 operates in user-mode 203. In other embodiments, the client agent 120 operates in user-mode 203 but interfaces via the interceptor 350 to a kernel-mode driver, process, service, task or portion of the operating system, such as to obtain a kernel-level data structure 225. In further embodiments, the interceptor 350 is a user-mode application or program, such as application.

In one embodiment, the interceptor 350 intercepts any transport layer connection requests. In these embodiments, the interceptor 350 execute transport layer application programming interface (API) calls to set the destination information, such as destination IP address and/or port to a desired location for the location. In this manner, the interceptor 350 intercepts and redirects the transport layer connection to a IP address and port controlled or managed by the interceptor 350 or client agent 120. In one embodiment, the interceptor 350 sets the destination information for the connection to a local IP address and port of the client 102 on which the client agent 120 is listening. For example, the client agent 120 may comprise a proxy service listening on a local IP address and port for redirected transport layer communications. In some embodiments, the client agent 120 then communicates the redirected transport layer communication to the appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain Name Service (DNS) request. In one embodiment, the client agent 120 and/or interceptor 350 resolves the DNS request. In another embodiment, the interceptor transmits the intercepted DNS request to the appliance 200 for DNS resolution. In one embodiment, the appliance 200 resolves the DNS request and communicates the DNS response to the client agent 120. In some embodiments, the appliance 200 resolves the DNS request via another appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may comprise two agents 120 and 120′. In one embodiment, a first agent 120 may comprise an interceptor 350 operating at the network layer of the network stack 310. In some embodiments, the first agent 120 intercepts network layer requests such as Internet Control Message Protocol (ICMP) requests (e.g., ping and traceroute). In other embodiments, the second agent 120′ may operate at the transport layer and intercept transport layer communications. In some embodiments, the first agent 120 intercepts communications at one layer of the network stack 210 and interfaces with or communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interface with a protocol layer in a manner transparent to any other protocol layer of the network stack 310. For example, in one embodiment, the interceptor 350 operates or interfaces with the transport layer of the network stack 310 transparently to any protocol layer below the transport layer, such as the network layer, and any protocol layer above the transport layer, such as the session, presentation or application layer protocols. This allows the other protocol layers of the network stack 310 to operate as desired and without modification for using the interceptor 350. As such, the client agent 120 and/or interceptor 350 can interface with the transport layer to secure, optimize, accelerate, route or load-balance any communications provided via any protocol carried by the transport layer, such as any application layer protocol over TCP/IP.

Furthermore, the client agent 120 and/or interceptor may operate at or interface with the network stack 310 in a manner transparent to any application, a user of the client 102, and any other computing device, such as a server, in communications with the client 102. The client agent 120 and/or interceptor 350 may be installed and/or executed on the client 102 in a manner without modification of an application. In some embodiments, the user of the client 102 or a computing device in communications with the client 102 are not aware of the existence, execution or operation of the client agent 120 and/or interceptor 350. As such, in some embodiments, the client agent 120 and/or interceptor 350 is installed, executed, and/or operated transparently to an application, user of the client 102, another computing device, such as a server, or any of the protocol layers above and/or below the protocol layer interfaced to by the interceptor 350.

The client agent 120 includes an acceleration program 302, a streaming client 306, a collection agent 304, and/or monitoring agent 197. In one embodiment, the client agent 120 comprises an Independent Computing Architecture (ICA) client, or any portion thereof, developed by Citrix Systems, Inc. of Fort Lauderdale, Fla., and is also referred to as an ICA client. In some embodiments, the client 120 comprises an application streaming client 306 for streaming an application from a server 106 to a client 102. In some embodiments, the client agent 120 comprises an acceleration program 302 for accelerating communications between client 102 and server 106. In another embodiment, the client agent 120 includes a collection agent 304 for performing end-point detection/scanning and collecting end-point information for the appliance 200 and/or server 106.

In some embodiments, the acceleration program 302 comprises a client-side acceleration program for performing one or more acceleration techniques to accelerate, enhance or otherwise improve a client's communications with and/or access to a server 106, such as accessing an application provided by a server 106. The logic, functions, and/or operations of the executable instructions of the acceleration program 302 may perform one or more of the following acceleration techniques: 1) multi-protocol compression, 2) transport control protocol pooling, 3) transport control protocol multiplexing, 4) transport control protocol buffering, and 5) caching via a cache manager. Additionally, the acceleration program 302 may perform encryption and/or decryption of any communications received and/or transmitted by the client 102. In some embodiments, the acceleration program 302 performs one or more of the acceleration techniques in an integrated manner or fashion. Additionally, the acceleration program 302 can perform compression on any of the protocols, or multiple-protocols, carried as a payload of a network packet of the transport layer protocol. The streaming client 306 comprises an application, program, process, service, task or executable instructions for receiving and executing a streamed application from a server 106. A server 106 may stream one or more application data files to the streaming client 306 for playing, executing or otherwise causing to be executed the application on the client 102. In some embodiments, the server 106 transmits a set of compressed or packaged application data files to the streaming client 306. In some embodiments, the plurality of application files are compressed and stored on a file server within an archive file such as a CAB, ZIP, SIT, TAR, JAR or other archive. In one embodiment, the server 106 decompresses, unpackages or unarchives the application files and transmits the files to the client 102. In another embodiment, the client 102 decompresses, unpackages or unarchives the application files. The streaming client 306 dynamically installs the application, or portion thereof, and executes the application. In one embodiment, the streaming client 306 may be an executable program. In some embodiments, the streaming client 306 may be able to launch another executable program.

The collection agent 304 comprises an application, program, process, service, task or executable instructions for identifying, obtaining and/or collecting information about the client 102. In some embodiments, the appliance 200 transmits the collection agent 304 to the client 102 or client agent 120. The collection agent 304 may be configured according to one or more policies of the policy engine 236 of the appliance. In other embodiments, the collection agent 304 transmits collected information on the client 102 to the appliance 200. In one embodiment, the policy engine 236 of the appliance 200 uses the collected information to determine and provide access, authentication and authorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 comprises an end-point detection and scanning mechanism, which identifies and determines one or more attributes or characteristics of the client. For example, the collection agent 304 may identify and determine any one or more of the following client-side attributes: 1) the operating system an/or a version of an operating system, 2) a service pack of the operating system, 3) a running service, 4) a running process, and 5) a file. The collection agent 304 may also identify and determine the presence or versions of any one or more of the following on the client: 1) antivirus software, 2) personal firewall software, 3) anti-spam software, and 4) internet security software. The policy engine 236 may have one or more policies based on any one or more of the attributes or characteristics of the client or client-side attributes.

In some embodiments, the client agent 120 includes a monitoring agent 197 as discussed in conjunction with FIGS. 1D and 2B. The monitoring agent 197 may be any type and form of script, such as Visual Basic or Java script. In one embodiment, the monitoring agent 129 monitors and measures performance of any portion of the client agent 120. For example, in some embodiments, the monitoring agent 129 monitors and measures performance of the acceleration program 302. In another embodiment, the monitoring agent 129 monitors and measures performance of the streaming client 306. In other embodiments, the monitoring agent 129 monitors and measures performance of the collection agent 304. In still another embodiment, the monitoring agent 129 monitors and measures performance of the interceptor 350. In some embodiments, the monitoring agent 129 monitors and measures any resource of the client 102, such as memory, CPU and disk.

The monitoring agent 197 may monitor and measure performance of any application of the client. In one embodiment, the monitoring agent 129 monitors and measures performance of a browser on the client 102. In some embodiments, the monitoring agent 197 monitors and measures performance of any application delivered via the client agent 120. In other embodiments, the monitoring agent 197 measures and monitors end user response times for an application, such as web-based or HTTP response times. The monitoring agent 197 may monitor and measure performance of an ICA or RDP client. In another embodiment, the monitoring agent 197 measures and monitors metrics for a user session or application session. In some embodiments, monitoring agent 197 measures and monitors an ICA or RDP session. In one embodiment, the monitoring agent 197 measures and monitors the performance of the appliance 200 in accelerating delivery of an application and/or data to the client 102.

In some embodiments and still referring to FIG. 3, a first program 322 may be used to install and/or execute the client agent 120, or portion thereof, such as the interceptor 350, automatically, silently, transparently, or otherwise. In one embodiment, the first program 322 comprises a plugin component, such an ActiveX control or Java control or script that is loaded into and executed by an application. For example, the first program comprises an ActiveX control loaded and run by a web browser application, such as in the memory space or context of the application. In another embodiment, the first program 322 comprises a set of executable instructions loaded into and run by the application, such as a browser. In one embodiment, the first program 322 comprises a designed and constructed program to install the client agent 120. In some embodiments, the first program 322 obtains, downloads, or receives the client agent 120 via the network from another computing device. In another embodiment, the first program 322 is an installer program or a plug and play manager for installing programs, such as network drivers, on the operating system of the client 102.

D. Dynamic Load Balancing

Referring now to FIG. 4A, an embodiment of a network of appliances for load balancing resources across branch offices is depicted. In brief overview, a plurality of appliances 200 are connected to and provide access to a plurality of branch offices 405A-405N. Each branch office may comprise a network 104 b and one or more servers 106. The plurality of appliances are connected via a network 104 a, by which they may communicate information corresponding to the appliances and the branch offices for load balancing purposes. Each appliance 200 may monitor the set of servers 106 to provide access, and report operational and performance characteristics of the network services 270 executing on the servers 106 to one or more other appliances 200.

Still referring to FIG. 4A, now in greater detail, in some embodiments, the appliances providing access to branch offices 200 may provide any of the functionality, operations and services of an appliance 200 described in conjunction with FIGS. 2A and 2B. The branch office appliances 200A-200N may provide acceleration 288, load balancing/switching 284, SSL VPN 280 and/or application firewall services 290 to any of the computing devices and users of its respective branch office 405A-405N. In one embodiment, each of the branch office appliances 200A-200N provide the same functionality, operations and service. In other embodiments, each of the branch office appliance 200 may provide different functionality, operations or services than another branch office appliance. For example, a first branch office appliance 200A may provide for SSL VPN 280 and acceleration 288, and a second branch office appliance 200B may provide load balancing/switching 284 with SSL VPN 280. A third branch office appliance 200N may provide only SSL VPN 280 and a fourth branch office appliance 200N, acceleration 288. Further to the example, a fifth branch office appliance 200B may provide acceleration 288 while a sixth branch office appliance 200C provides application firewall 290 functionality.

Although branch office appliances 200 are generally described as an appliance 200 in a branch office 405, the branch office appliance 200 may be an appliance 200 deployed at any location in a network. For example, a branch office appliance 200 may be deployed at a data center. In another example, a branch office appliance 200 may be deployed on a subnet or network segment of a corporate LAN 104. In another embodiment, a branch office appliance 200A may be deployed on a first corporate LAN and a second branch office appliance 200B on a second corporate LAN. So, although the appliance 200 is described in FIG. 4A as a branch office appliance 200, it is not limited to operations only at a branch office 405.

In one embodiment, a branch office appliance 200 requests operational or performance information from or otherwise monitors each of the servers 106 or network services 270 it provides access to. In some embodiments, the branch office appliance 200 requests information upon establishment of the connection to a server 106. In another embodiment, the branch office appliance 200 requests information or otherwise monitors a network service 270 on a predetermined frequency, such as every 1 sec, or 1 msec. For example, a branch office appliance 200 may poll each of its connected servers 106 every 1 sec for availability. In some embodiments, a branch office appliance 200 requests availability information from connected network services 270 over a predetermined time period, such as every 1 sec for an hour. In yet another embodiment, a branch office appliance 200 requests information from connected servers 106 upon an event, such as receiving a request from a client 102, or receiving a DNS request. The information requested may comprise any operational or performance characteristic. In some embodiments, an appliance 200 may use one or more monitoring agents to monitor a network service 270, as will be discussed in detail with respect to FIG. 4B.

In some embodiments, the operational and/or performance characteristic information 410 includes information on any of the following for a network service 270: 1) load, 2) numbers and types of connections, 3) resource usage, 4) resource availability, 5) number of requests outstanding, 6) number of requests transmitted, 7) number of clients servicing, 8) response time information, including average and historical response times, 9) errors, status, performance or bandwidth of a connection, 10) number of sessions, and states or status thereof, and 11) a weight assigned to the server.

In one embodiment, a branch office appliance 200 may calculate or be configured with an assigned weight for a network service 270, and the weight may subsequently be used for load balancing purposes. This weight may be calculated or configured in response to any of the performance characteristics described above. A weight may be an integer, decimal number, or any other type of numeric indicator. In some embodiments, weights may be assigned to network services 270 based on the capacity of the server hosting the service. In one embodiment, an appliance may be preconfigured with the capacities of the network services 270 of the branch office to which it provides access, and may calculate weights based on these capacities. In another embodiment, an appliance may query a network service 270 to determine the service's capacity.

In one embodiment, the weight assigned to a network service 270 may reflect a ratio of the network service 270 capacity as compared to the capacity of at least one other network service 270. For example, two network services 270 having equal capacities of servicing 1000 requests per second may be assigned equal weights. Or for example, a network service 270 having a capacity of servicing 1000 requests per second may be assigned a weight corresponding to half the weight assigned to a network service 270 capable of servicing 2000 requests per second. Or for example, a network service 270 having a capacity of 3000 requests/second might be assigned a weight of 5, a network service 270 having a capacity of servicing 6000 requests/second might be assigned a weight of 10, and a network service 270 having a capacity of servicing 9000 requests/second might be assigned a weight of 15. Or, for example, weights may be assigned to network services 270 by dividing the network service's capacity by a fixed number.

In another embodiment, weights may be assigned to servers based on server capacity minus load. In this embodiment, the weight represents the available capacity for the server. For example, a first network service 270 capable of handling 2000 requests per second, and which has a current average load of 1500 requests per second may have an available capacity of 500 requests/second. A second network service 270 capable of handling 2000 requests per second, and which has a current average load of 1000 requests per second may have an available capacity of 1000 requests/second. The second network service 270 may be assigned a weight double the weight of the first network service 270, reflecting that it has twice the available capacity.

In one embodiment, the appliances 200 receive information from a respective branch office appliance via a local area network connection. In some embodiments, the branch office appliances 200 establish or communicate via a transport layer connection, such as a TCP or UDP connection. In other embodiments, the branch office appliances 200 maintain a connection with each other. In other embodiments, the branch office appliances 200 establish connections to each other on an as needed basis, e.g., connect and reconnect when they need to communicate.

In one embodiment, a first branch office appliance 200A transmits, to a second branch office appliance 200, weight or availability information corresponding to one or more network services 270. The second branch office appliance 200B stores the received information. In some embodiments, this received information is aggregated or combined with information received from other branch office appliances 200. The branch office appliances 200A-200N may exchange or provide information once, or on a predetermined frequency, such as every 1 msec or 1 sec. In some embodiments, the first and second branch office appliances 200 use a request/reply messaging mechanism or protocol to transmit information to each other. In other embodiments, the first and second branch office appliances 200 have a custom or proprietary exchange protocol for exchanging information.

In some embodiments, a branch office appliance 200 establishes a connection or communicates with a predetermined number of other branch office appliances 200. In other embodiments, the branch office appliance 200 collects and aggregates information from a predetermined number of branch office appliances 200. In one embodiment, the predetermined number of branch offices is 31. In another embodiment, the predetermined number of branch offices is 32. In yet other embodiments, the predetermined number of branch offices is 16, 48, 60, 96, 128 or 256. In a further embodiment, the predetermined number of branch offices is 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200 or 250. The number of branch offices a branch office appliance 200 may connect to or collect information from may depend on the operational or performance characteristics of the network 104 a, the appliance 200, the branch offices 405, and branch office networks 104 b along with the applications, data, and resource usage of the users across branch offices. In some embodiments, the predetermined number of branch office appliances 200 may not be set or configured, or otherwise limited only by the memory, capacity and performance of the branch office appliance 200.

In another embodiment, a branch office appliance 200 requests information from each of the branch office appliance 200 it is connected to. In some embodiments, the branch office appliance 200 requests information upon establishment of the connection to another branch office appliance 200. In another embodiment, the branch office appliance 200 requests information from another branch office appliance 200 on a predetermined frequency, such as every 1 sec, or 1 msec. For example, a branch office appliance 200 may poll each of its connected branch office appliances 200A-200N every 1 sec for information 410. In some embodiments, a branch office appliance 200 requests information 410 from another branch office appliance 200 over a predetermined time period, such as every 1 sec for an hour. In yet another embodiment, a branch office appliance requests information 410 from a branch office appliance 200 upon an event, such as receiving a request from a client 102, or receiving a DNS request.

The information transmitted among the branch office appliances 200 may comprise any type and form of data, statistics, status or information related to or associated with the operational and/or performance characteristics of a branch office appliance 200, a network 104 of the branch office appliance 200, and/or any connection to a branch office appliance 200, such as via a client 102, server 106 and network service 270. In some embodiments, the information 410 comprises operational and/or performance data on any client 102, server 106, or network service 270 connected to the branch office appliance 200. In one embodiment, the branch office appliance 200 determines operational and/or performance information about any network service 270 it is connected to or servicing, and creates information on these network services 270. In this embodiment, the branch office appliance 200 may provide this information 410 to the other branch office appliances 200.

Referring now to FIG. 4B, a block diagram of an appliance using a plurality of monitoring agents to monitor a network service is shown. In brief overview, an appliance 200 comprises a plurality of monitoring agents 420. Each of the plurality of monitoring agents is assigned to monitor a service 270. In one embodiment, each of the plurality of monitoring agents may be assigned a weight. Monitoring agents 420 may also be referred to as probes or load monitors.

Still referring to FIG. 4B, an appliance comprises a plurality of monitoring agents 420. A monitoring agent may comprise any program, script, daemon, or other computing routine that reports a performance or operational characteristic of a network service 270 to the appliance 200. A monitoring agent may communicate with a network service 106 once, or on a predetermined frequency, such as every 1 msec or 1 sec. In some embodiments, a monitoring agent may use a request/reply messaging mechanism or protocol with the server. In other embodiments, a monitoring agent 402 may have a custom or proprietary exchange protocol for communicating with the server. In some embodiments, a single monitoring agent may monitor a plurality of servers. In other embodiments, a plurality of agents may monitor a single server. In still other embodiments, a plurality of monitoring agents may each monitor a plurality of servers, wherein each of the plurality of servers is monitored by a plurality of monitoring agents.

In the embodiment shown, the one or more monitoring agents 420 are associated with one or more network services 270. In other embodiments, the one or more monitoring agents may monitor an appliance 200, vServer, network service 270, client, or any other network resource. In one embodiment, a user specifies a type of network service to associate with the one or more monitoring agents 420. In another embodiment, a user customizes a monitoring agent. In still another embodiment, a generic monitoring agent 420 is used. In yet another embodiment, the one or more monitoring agents 420 determine the response time of the one or more network services 270 for responding to a request of one of the following types: ping, transport control protocol (tcp), tcp extended content verification, hypertext transfer protocol (http), http extended content verification, hypertext transfer protocol secure (https), https extended content verification, user datagram protocol, domain name service, and file transfer protocol.

In some embodiments, the one or more monitoring agents 420 are protocol-specific agents, each agent determining availability for a network service of a particular protocol-type. In some embodiments, a monitoring agent 420 determines a response time of a server 106 or network service 270 to a TCP request. In one of these embodiments, the agent uses a “TCP/ICMP echo request” command to send a datagram to the network service 270, receive a datagram from the network service 270 in response, and determine a response time based on the roundtrip time of the datagram. In another of these embodiments, the monitoring agent 420 verifies that the response from the network service 270 included expected content and did not contain errors.

In other embodiments, a monitoring agent 420 determines availability of a network service 270 to a UDP request. In one of these embodiments, the agent uses a “UDP echo” command to send a datagram to the network service 270, receive a datagram from the network service 270 in response, and determine a response time based on the roundtrip time of the datagram. In another of these embodiments, the monitoring agent 420 verifies that the response from the network service 270 included expected content and did not contain errors.

In still other embodiments, the monitoring agent 420 determines availability of a network service 270 to an FTP request. In one of these embodiments, the monitoring agent 420 sends an FTP command, such as a “get” command or a “put” command, to the network service 270 and determines a time needed by the network service 270 to respond to the command. In another of these embodiments, the monitoring agent 420 verifies that the response from the network service 270 included expected content, such as contents of a file requested by a “get” command, and did not contain errors.

In yet other embodiments, the monitoring agent 420 determines availability of a network service 270 to an HTTP request. In one of these embodiments, the monitoring agent 420 sends an HTTP command, such as a “get” request for a uniform resource locator (URL) or a file, to the network service 270 and determines a time needed by the network service 270 to respond to the request. In another of these embodiments, the monitoring agent 420 verifies that the response from the network service 270 included expected content, such as the contents of a web page identified by the URL, and did not contain errors.

In further embodiments, the monitoring agent 420 determines availability of a network service 270 to a DNS request. In one of these embodiments, the monitoring agent 420 sends a DNS request, such as a dnsquery or nslookup for a known network address, to the server 106 or network service 270 and determines a time needed by the server 106 or network service 270 to respond to the request. In another of these embodiments, the monitoring agent 420 verifies that the response from the network service 270 included expected content, such as the domain name of a computing device 100 associated with the known network address, and did not contain errors.

A monitoring agent 420 may be assigned a weight by a network appliance 200. A weight may comprise an integer, decimal, or any other numeric indicator. In some embodiments, a user may configure the weight corresponding to a given monitoring agent 420. In some embodiments, all monitoring agents may be assigned equal weight. In other embodiments, a plurality of monitoring agents may each be assigned different weights. The weights may be assigned to the monitors based on any criteria indicating relative importance, including without limitation importance of the monitored service, reliability of the monitoring mechanism, and the frequency of monitoring.

In one embodiment, a monitoring agent may be assigned a weight based on the relative importance of the service the appliance monitors. For example, if most user requests in a given environment were HTTP requests, a monitoring agent monitoring HTTP availability of a server 106 might be assigned a weight of 10, while a monitoring agent monitoring FTP availability of a server 106 might be assigned a weight of 3. Or, for example, if an administrator placed a high priority on UDP applications, a monitoring agent monitoring UDP availability of a server may be assigned a weight of 20, while a DNS monitoring agent may be assigned a weight of 5.

In some embodiments, an appliance 200 may compute a sum of the weights of the monitoring agents currently reporting a network service 270 as operational. For example, if five monitoring agents, each assigned a weight of 30, are monitoring a network service 270, and three of the five monitoring agents report the network service 270 as available, the appliance may determine the sum of the monitoring agents currently reporting the network service 270 as operational to be 90. Or for example, if only two monitoring agents, one with a weight of 20 and the other with a weight of 40, are reporting a server 106 as available, the appliance may compute the sum of the monitoring agents currently reporting a server 106 as operational to be 60.

E. Health Based Spillover

Referring now to FIGS. 5A and 5B, systems and methods for managing spillover from a first virtual server to a second virtual server based on health are depicted. The appliance may establish or user configure a health threshold for one or more virtual servers managing one or more services. The health threshold may be established or identified as a percentage. The appliance monitors the health of the services used by a virtual server. In response to detecting the health falling below the established health threshold, the appliance dynamically directs client requests to another virtual server. The health threshold may be adjusted to take into account capacity, response times, virtual server performance or performance of the server. The appliance manages virtual servers based on health to maintain performance of the virtual servers and the services managed by the virtual servers at a desired level or within a predetermined performance range.

Referring now to FIG. 5A, an embodiment of an appliance or intermediary for providing virtual server spillover management based on health is depicted. In brief overview, the appliance 200 establishes a first vServer 275A to manage access by a plurality of clients 102 a-102 n to one or more services 270A-270N of a first set of servers 106A-106N. The appliance 200 includes a connection management mechanism 710 or connect manager for managing and balancing requests from clients 102 a-102 n to one or more set of services 270A-270N via one or more vServers 275A-275N. The appliance 200 establishes for a first vServer 275A a health threshold 720A, which may be specified by a user. The appliance may establish a second vServer 275N with a second health threshold 720B. Via monitoring agents 420A-420N, the appliance monitors the operational status of each of the services 270A-270N. The monitoring agents 420 may include a health monitor 702 for measuring the health used by a virtual server 275. The health monitor 702 may at predetermined frequencies or time frames determine a measured health 725A for a first vServer 275A. The health monitor 702 may also determine a measured health 725B for the second vServer 275N.

If the measured health for the first vServer 275A is determined to have reached or fallen below the health threshold 720A, the connection manager 710 of the appliance may determine to direct client requests to the second vServer 275N. For example, a user may configure a health threshold at 50%. If the health detector 720 determines the measured health 725 of the vServer 275 falls below 50%, the appliance 200 via the connection management mechanism 710 may switch client requests to the second vServer 275N.

Each of the vServers 275A-275 n may identify or be configured to identify the one or more services the vServer is managing. In some embodiments services may be organized or configured into a group referred to as a service group or group of services. In some of these embodiments, a command, instruction, policy or configuration may be applied to each service in a service group by referencing the service group via the command, instruction, policy or configuration. In some embodiments, a service or a service group may be enabled or disabled by an administrator of the appliance. In other embodiments, a service or service group may be enabled or disabled by any component of the appliance, such as connection manager 710 or a monitoring agent 420. In some embodiments, a service or service group may be referred to or considered a member of the vServer. In some embodiments, to have a service or service group be managed by a vServer, the service or service group may be bound to the vServer via any type and form of bind command or instruction. In some of these embodiments, a service may be referred to as bound to a vServer. In some embodiments, a service may be enabled or disabled but not bound to the vServer. In other embodiments, a service may be bound to a vServer but disabled.

Any of the services 270A-270N′ and/or service groups may be assigned any type and form of weight 770, such as any of the weights described in conjunction with FIGS. 4A and/or 4B. The weight may be any type and form of numerical factor identifying a relative degree of importance, influence, consideration or value. In some embodiments, each service may be assigned the same weight. In other embodiments, each service may be assigned a different weight. In some embodiments, some services are assigned the same weight while other services are assigned different weights. In one embodiment, a same or different weight may be assigned to any service group. In some embodiments, the weight assigned to a service group is assigned at the group level. For example, the service group may be considered a single entity with the assigned eight. In other embodiments the weight assigned to a service group is assigned to each of the services of the service group. For example, the services in the service group may be treated as separate entities each with the same weight assigned to the service group. In some embodiments, a sum of the weights 770 assigned to a service and/or service group may be equal to 100. In other embodiments, a sum of the weights 770 assigned to a service and/or service group may be any predetermined number greater than or less than 100.

In some embodiments, a service and/or service group may be assigned a different weight based on state: up/down (active/inactive), enabled/disabled, etc. In one embodiment, a service may have a first weight for an up state. In some embodiments, the service may have a second weight for a down state. In some embodiments, a service and/or service group may be assigned a different weight based on load. In another embodiment, the a service and/or service group may be assigned a progressively changing weight based on changes in state and/or load.

The health 725A-725B, generally referred to as health 725, may be defined as a percentage of weights of services that are currently in an up state, sometimes referred to as active, to the sum total of the weights of all enabled services, such as those services that are either in an up or down state. The down state is sometimes referred to as inactive. From a computational perspective, the health 745 may be expressed or represented in logic or executable form as: Health of a virtualServer=[(activeWeight of virtualServer)/totalWeight of virtualServer)]*100 where:

-   -   activeWeight of services for vServer 275=sum of weights of         services and/or service groups that are (a) active and, in some         embodiments, also (b) enabled     -   totalWeight(virtual server)=sum of weights of services and/or         service groups of the vServer 275 that are enabled.

The activeWeight parameter, input or value to the health determination may comprise the addition or summation of each of the weights assigned to each service and/or service group that is identified as in a predetermined state. In one embodiment, the predetermined state is up or active. The activeWeight value may be set to a resulting total of the addition or summation. In some embodiments, the service and/or service group must be enabled and in the predetermined state to be included in the addition or summation. In some embodiments, the service and/or service group must be bound and in the predetermined sate to be included in the addition or summation.

The totalWeight parameter, input or value to the health determination may comprise the addition or summation of each of the weights assigned to each service and/or service group that is assigned to the vServer. In some embodiments, those service and/or service groups that are enabled are included in the totalWeight computation. In some embodiments, those service and/or service groups that are bound to the vServer are included in the totalWeight computation. in some embodiments, those service and/or service groups that either have an up or down state are included in the totalWeight computation The sum of weights of services and/or service groups that are enabled may include all services that are either identified as ‘UP’ or ‘DOWN’. In some embodiments, the sum of weights of services and/or service groups that are enabled may not includes those services which are marked disabled or otherwise configured to be disabled.

In some embodiments, the health is expressed numerically. In other embodiments, the health is expressed as text or string format. In some embodiments, health is expressed as a percentage, in the form X %, XX %, XXX %, In some embodiments, the range of health is from 0% to 100%. In some embodiments, health may be expressed as a percentage with any number of decimal places, such as X.X %, XX.XX % or XXX.XXX %. In other embodiments, health is expressed without multiplying by a 100 in the above equation. In these embodiments, health may be expressed as a percentage greater than 100%. In other embodiments, the health may be a number. In some embodiments, health may be a ratio. In one embodiment, health may be a fraction. In some embodiments, health may be a decimal.

The health monitor 702, sometimes referred to as a health detector or detector, includes or provides logic, business rules, functions or operations for determining the health of one or more virtual servers 275. The health detector 702 may include software, hardware or any combination of software and hardware. The health detector 702 may comprise an application, program, script, library, process, service, driver, task, thread or any type and form of executable instructions. In some embodiments, the health monitor is a monitoring agent. In another embodiment, the health monitor is part of a monitoring agent. In still another embodiment, the health monitor may be part of the vServer. In yet another embodiment, the health monitor may be a separate component of the appliance in communication with any one or more of the monitoring agent, vServer and/or connection manager.

In some embodiments, the health detector 702 determines or computes the health 720. The health detector 702 may determine the health on a predetermined frequency. In some embodiments, the health detector 702 determines an average health over any period of time In other embodiments, the health detector 702 measures the health 725 for a vServer 275 based on the number of packets on a queue waiting to be transmitted. In some embodiments, the health detector 702 determines health upon the transition of a queue of network packets from empty to non-empty and vice-versa. In some embodiments, the health detector 702 determines health upon receipt of a client request. In some embodiments, the health detector 702 determines health upon receipt of a server response.

The health detector 702 may determine the health of a vServer responsive to any one or more monitoring agents. For example, in some embodiments, the health detector may compute/recompute the health upon return of a status of a service from a monitoring agent. In another embodiment, the health detector may compute/recompute the health upon a change in status of a service from a monitoring agent. In some embodiments, the health detector may determine the health at a configured or configurable predetermined frequency. In some embodiments, the health detector may determine the health at different times or different frequencies for each vServer. In yet another embodiment, the health detector may use different health computations among a plurality of vServers. For example, in some embodiments, the type and form of the health computation may be configurable or specified by policy.

In some embodiments, the health detector 702 determines, computes or establishes the totalWeight of health a first time and updates the totalWeight of services upon a change in the enabled or disabled state of a service or service group. In some embodiments, the health detector 702 determines, computes or establishes the totalWeight of health a first time and updates the totalWeight of services upon a change in the weight of any of a service or service group. In other embodiments, the health detector 702 determines, computes or establishes the totalWeight any type a health determination or computation is made.

The health threshold 720 for a vServer 275 may be specified as a number, such as a real or integer. In some embodiments, the health threshold 720 may be expressed as a percentage. In other embodiments, the health threshold 720 may be expressed as a ratio or a decimal. For example, the health threshold 720 may represent a percentage of enabled services active and used by the vServer 275. In another example, the health threshold 720 may represent a percentage of health available to the vServer 275. In some embodiments, the health threshold may be expressed logically using any type and form of expression, such as for example, “health <20%”.

In some embodiments, the health threshold 720 may indicate a relative percentage from a predetermined point. In one embodiment, the health threshold 720 identifies an amount of change of the measured health. For example, the health threshold 720 may represent an amount of decrease in percentage of health to be considered triggering the threshold. In another embodiment, the health threshold 720 may indicate an average health value to maintain. In some embodiments, the health threshold 720 may indicate an average health value over a period of time. In other embodiments, the health threshold 720 may indicate a relative percentage of services that change from an active to inactive state or from an up to a down state.

The connection management mechanism 710, also referred to as a connection manager or a virtual server switch, comprises software, hardware, or any combination of software and hardware having logic, functions or operations for receiving and managing requests, connections and communications from one or more clients 102A-102N. In one embodiment, the connection manager 710 receives or intercepts transport layer connection requests and/or communications between the clients 102A-102N and one or more services 270A-270N. The connection manager 710 may include an application, program, service, process, task, thread or any type and form of executable instructions. In response to receiving a client communication, the connection manager 710 identifies, determines or selects a vServer 275 for processing a received communication from a client 102.

The connection manager 710 may operate responsive to the load monitor 420 and/or the health detector 702. The load monitor 420 may monitor the measured health 725. In some embodiments, the load monitor 420 and/or health detector 702 measures the health on a predetermined frequency. In one embodiment, the load monitor 420 and/or health detector 702 measures the health responsive to any events, such as receipt of a network packet. In other embodiments, the load monitor 420 and/or health detector 702 may determine whether or not the measured health 725 is less than the health threshold 720.

If the connection manager 710 determines from the load monitor 420 and/or health detector 702 that the measured health 725 of a first vServer 275A falls below the health threshold 720, the connection manager 710 directs client requests for the services managed by the first vServer 275A to a second vServer 275 n. The second vServer 275 n may be configured or established as backup server to the first vServer 275A. For example, the first vServer 275A may be designated a primary vServer 275A and the second vServer 275N as backup vServer 275N. In another embodiment, the second vServer 275N may be another virtual server—primary, redundant, or otherwise—for managing the services 270A-270N. In yet another embodiment, the second vServer 275N is configures or designated as the spillover virtual server for the first vServer 275A. In some cases, the second vServer 275N is established upon determining the first vServer 275275A fall below the health threshold 720. In other cases, the vServer 275N is already operating or executing on the appliance 200.

In some embodiments, the connection manager 270 directs new client request requests to the second vServer 275. In one embodiment, if the request is from a connection already established with the first vServer 275A, the connection manager 710 may direct the request to the first vServer 275A even if the health threshold 720 is exceeded or fallen below. This may be referred to as connection or session persistence. In another embodiment, the connection manager 710 directs any client requests to the second vServer 275, for example, even a request of a previously established connection.

In one embodiment, the connection manager 710 directs client requests to the second vServer 275N while the first vServer 275 has a measured health 725 greater than the health threshold 720. In another embodiment, the connection manager 710 directs clients requests back to the first vServer upon determining that the measured health 725 of the first vServer 275 has increased above the health threshold 720. In some embodiment, the connection manager 710 determines which of the first vServer 275A and the second vServer 275N has the highest health or is the least nearest to the corresponding health threshold 720 and directs the client requests to the determined vServer. In other embodiments and in the case of multiple vServers 275A-275N falling below a health threshold 720, the connection manager 710 determines which vServer 275A-275N falls below its corresponding threshold 720 the least and directs the client requests to the determined vServer.

Upon detecting the health threshold 720 has been reached for the first vServer 275A and/or the second vServer 275N, the connection management mechanism 710, in one embodiment, may determine not to establish another spillover vServer 275N but instead redirects the client 102 directly to a server 106 or otherwise to bypass the appliance 200. For example, the connection management mechanism 710 may determine the health threshold 720B for the spillover vServer 275N has been reached and may redirect the client 102 to bypass the appliance 200 instead of establishing a third vServer 275N for spillover. In these embodiments, the connection management mechanism 710 may transmit a redirect Uniform Resource Locator (URL) 760 to the client 102 for the client 102 to connect to in response to the client's connection request. The URL 760 may identify any one of the servers 106 or services 270.

In some embodiments, the appliance 200 via a load monitor 420 and/or health detector 702 measures and monitors the health of the second virtual server 275N. The second vServer 275N may have the same health threshold 720 or a different health threshold 720 as the first vServer 275A. If the connection manager 710 determines from the load monitor 420 and/or health detector 702 that the measured health 725N of the second vServer 275N falls below the health threshold 720, the connection manager 710 directs client requests for the services managed by the second vServer 275A to another vServer 275N, such as the first vServer 275A or a third vServer 275B. The second vServer 275N may have a third vServer 275B designated as backup virtual server or a spillover virtual server. The health threshold management techniques described herein may be used for a chain or plurality of virtual servers and spillover virtual servers, each with a health threshold and designated backup or spillover virtual server.

The appliance via the connection manager directs client requests to the primary vServer 275 or any backup or spillover vServer 275 based on measured health 725 in view of the established health threshold 720. The appliance 200 may dynamically adjust any health threshold 720 for any vServer 275 based on any performance or operational characteristics of the appliance, vServer, bandwidth, network connection, client or server. In one embodiment, the appliance may determine that the established health threshold 720 is set relatively low in comparison to the measured health 725 and determines to dynamically increase the health threshold 720. For example, the appliance may adjust to the health threshold 720 within a certain percentage or threshold of the measured health. In another embodiments, the appliance may determine that the established health threshold 720 is set relatively high in comparison to the measured health 725 and determines to dynamically decrease the health threshold 720.

In one case, the appliance 200 dynamically sets or establishes a health threshold 720 by measuring health 725 of a vServer 275 for a predetermined time period. For example, upon startup of a vServer 275, the health detector 702 may measure health for a predetermined or configured time period, and then based on an average, peak or range of health measurements set the health threshold 720. In another case, the appliance 200 may dynamically adjust a health threshold 720 based on adding or removing services 270A-270 n managed by a vServer 275. In still other embodiments, the appliance 200 may dynamically adjust the health threshold 720 of a vServer 275 based on information and feedback from a monitoring agent 197 and/or monitoring service 198. In still other embodiments, the appliance 200 may dynamically adjust health thresholds 720 based on one or more policies of a policy engine 195.

In some embodiment, the appliance 200 excludes a vServer 275 from a load computation or determination, or otherwise a load balancing decision if the health 725 of the vServer 275 falls below the health threshold 720. In these embodiments, this may be done so that the other vServer 275A-275N which carry the load for the excluded vServer 275 do not also become overloaded. In other embodiments, the appliance 200 adjusts a weight used for the vServer 275 upon detecting the vServer's bandwidth 725 exceeds the health threshold 720. For example, the weight of the vServer 275 may be adjusted to minimize the impact to the other vServer 275A-275N for not having the vServer 275 available to also service requests.

In some embodiments, the appliance or any component thereof may adjust any one or more weight of any one of the services or service groups and then recompute the health. The appliance 200 may dynamically adjust any weight any service or service group based on any performance or operational characteristics of the appliance, vServer, bandwidth, network connection, client or server.

Referring now to FIG. 5B, an embodiment of steps of a method for practicing dynamic virtual server spillover management based on health is depicted. In brief overview, at step 505, the appliance establishes a first virtual server 275A which directs requests from a plurality of clients to a plurality of services. At step 510, the appliance establishes a health threshold for the first virtual server. At step 515, the appliance monitors a status for each of the plurality of services. At step 550, the appliance measures and monitors the health 725 of the first vServer 275. At step 525, the appliance receives a client request. At step 530, the appliance determines whether or not the health threshold for the first vServer 275A has been exceeded. If not, at step 535, the appliance directs the client request to the first vServer 275A. If the threshold has been exceeded, the appliance at step 540 determines whether or not to establish or use a second vServer 275N or provide a redirect URL to the client 102. In one case, at step 545, the client is redirected to the service and bypasses the first vServer 275A. At step 550, the appliance may determine if the client is persistent (referred to as being sticky) with the first vServer 275A or the second vServer 275N. If the client is sticky to the first vServer 275A, the appliance may direct the request to the first vServer 275A at step 535. Otherwise, the appliance spills over to an established second vServer 275N at step 555. The method may continue at step 510 to monitor and perform health based spillover management for the second vServer 275N.

In further detail, at step 505, an appliance establishes a first virtual server 275 which manages connections and direct requests from a plurality of clients to a first plurality of services 270. In one embodiment, the appliance may establish the virtual server upon startup of the appliance. In another embodiment, the appliance may establish the virtual server in response to a previously established virtual server exceeding maximum connection threshold. In one embodiment, the appliance may establish a plurality of virtual servers. In some embodiments, a user configures and starts the first vServer 275. In other embodiments, the first vServer is configured, established or designed by the appliance or a user as a primary virtual server.

At step 510, the appliance may establish or otherwise provide a health threshold 720 for the first vServer 275. In one embodiment, the health threshold 720 may be initially configured by a user or administrator of the appliance. In another embodiment, the health threshold 720 may be initially determined by the appliance by monitoring the health of the vServer 275 or by polling one or more services 270. In some embodiments, the appliance 200 may use a default or predetermined health threshold 720. For example, the appliance may use a predetermined health threshold 720 associated with or based on the type of service 270.

At step 515, the appliance may monitor a status for each of the services 270 using any means. In one embodiment, the appliance may use a monitoring agent 420. In another embodiment, the appliance may use a plurality of monitoring agents 420. In one embodiment, the appliance may monitor the status for each of the services at predetermined time intervals, for example once every 0.01, 0.1, 0.2, 0.5, or 1 seconds. In another embodiment, the appliance may monitor the status for each of the services 270 asynchronously or based on any events.

At step 520, the appliance measures and monitors the health of the first vServer 275A. The load monitor 420 and/or health detector 702 may compute, determine or otherwise make health measurements 725. In one embodiment, the appliance determines the measured health 725 of a vServer 275 on a predetermined frequency. In another embodiment, the appliance determines the measured health 725 of a vServer 275 triggered by an event. In one case, the appliance determines the measured health 725 of a vServer 275 at the request of a user. In some embodiments, the appliance 200 measures health as a percentage using any of the health computations described in connection with FIG. 5A. In some embodiments, the appliance may dynamically adjust the health threshold 720 based on health measurements. In other embodiments, the appliance may dynamically adjust the health threshold 720 based on performance and/or operational characteristics of the appliance, the vServer 275, the network connection, and/or the service 270.

At step 525, the appliance may receive a client request. In one embodiment, the appliance intercepts the client request as a transparent interception device. In another embodiment, the client transmits the request to the appliance as a proxy. In some embodiments, the appliance receives a client request to open or establish a transport layer connection. In other embodiments, the appliances receives a client request to access a service via a previously established transport layer connection. The transport layer request may be received from any computing device including a client 102, server 106, or a second appliance 200. In one embodiment, the request may identify a type of service 270. For example, the request may comprise a request for HTTP service. Or, for example, the request may comprise a request for UDP service.

At step 530 the appliance may determine whether the measured health 725 for a vServer 275 has reached or fallen below the health threshold 720. The appliance may compare the current measured health 725 for the first virtual server with the current value of the health threshold 720 for the first virtual server. In other embodiments, the load monitor 420 and/or health detector 702 may have already determined the health threshold 725 for the vServer 275 has been reached or exceeded. In another embodiment, the appliance 200 may determine if the health threshold 725 has been reached responsive to receiving the client request. If the health threshold 720 of the first virtual server has not been reached, the appliance may provide the client request to the first virtual server at step 535.

If the appliance determines the health threshold 720 of the first virtual server has been reached, the appliance may establish, use or otherwise spillover to a second virtual server 275N at step 540. In other embodiments, a second virtual server 275N may already have been established prior to some or any of the steps shown. In another embodiment, the second virtual server 275N may be established responsive to determining the health threshold 720 has been reached. The second virtual server may provide access to a second plurality of services 270. In one embodiment, one or more of the second plurality of services 270 may comprise the same type of service 270 as one or more of the first plurality of services. The appliance may then establish and/or adjust a health threshold 720 for the second virtual server. The appliance may provide the client request to the second virtual server 275 at step 555.

In other embodiments, if the health threshold 720 of the first virtual server has been reached, the appliance may redirect the client making the request to another resource. In one embodiment, the appliance may transmit a URL to the client comprising the address of a server 106 or service 270 such that the client may bypass the appliance 200 and access the server 106 or service 270 directly. In one embodiment, the appliance may transmit a URL to the client comprising the address of a second appliance 200. In still another embodiment, the appliance 200 may redirect the client request to a second appliance.

In another embodiment, the appliance identifies that the measured health exceeds the health threshold and directs client requests to the first vServer. In some embodiments, the appliance identifies that one or more services that were previously down and the measure health now exceeds the health threshold. In response to the health reaching or being above the health threshold, the appliance may direct client request to the first vServer instead of the second vServer.

At step 550, the appliance 200 may determine whether the client making the request has a previously existing connection or session with either the first or a second virtual server. In some embodiments, an appliance may assign a priority to providing requests from a client to virtual servers that have previously serviced or are currently servicing connections or session from the client. For example, if a request is received from a client, and the client has a currently existing connection with a first virtual server, the appliance 200 may provide the request to the first virtual server even if the first virtual server has reached or exceeded the bandwidth threshold. Or, for example, if a client has a previous connection via a backup virtual server, and the primary virtual server subsequently falls below the health threshold 720, the appliance 200 may still provide a subsequent request from the client to the backup virtual server. In one embodiment, a connection management mechanism 710, or other appliance component may track previously established or current connections or session so that incoming requests from a client can be provided to a virtual server having previously serviced the connection or session from the client.

At step 555, the appliance 200 may dynamically manage virtual spillover based on health by directing or providing the client request to the spillover or second vServer 275N. In some embodiments, the appliance determines the second vServer 275 is busy, unavailable or has exceeded its health threshold or another threshold. In response, the appliance may redirect the client at step 540 or provide the client request to a third vServer 275B or another appliance 200′. In some embodiments, the appliance has a plurality of vServers 275A-275N managing the services 270 and determines which vServer to direct the client request based on comparison of each vServer's measured health and/or health threshold. In one case, the appliance provides the client request to one of a plurality of backup or spillover vServers based on the best measured health. In another case, the appliance provides the client request to the vServer with the greatest difference between the measured health and the health threshold.

Although an embodiment of method 500 is generally described above in regards to measuring and monitoring health of a first vServer and spilling over to a second vServer, any steps of the method may be performed for the second vServer and a spillover server for the second vServer, and for a third vServer, and so on. An embodiment of method 500 or any steps thereof may be practiced for a plurality of virtual servers, such as a set of primary vServer managing the same or different services. Another embodiment of method 500 or any steps thereof may be practiced for a chain of spillover virtual servers, so that a second vServer spills over into a third vServer based on health and so on. 

What is claimed:
 1. A method for a device intermediary to a plurality of clients and a plurality of services to determine a health of a virtual server, the method comprising: (a) establishing, by a device intermediary to a plurality of a clients and a plurality of services executing on one or more servers, a virtual server to manage the plurality of services, each service of the plurality of services has a configuration on the device that specifies a weight and whether the configuration is enabled or disabled; (b) identifying, by the device via monitoring of the plurality of services, that a service of the plurality of services, with a configuration that is disabled, has a status of up; and (c) determining, by the device for the virtual server, a health comprising a first sum of each weight specified by the configuration on the device for each of the plurality services that has the status of up divided by a second sum of each weight specified by the configuration on the device for each of the plurality of services for which the configuration is enabled, the second sum excluding the weight of the service with the configuration that is disabled.
 2. The method of claim 1, wherein step (a) further comprises receiving, by the device, specification of the weight for the configuration of at least one service of the plurality of services from a user.
 3. The method of claim 1, wherein step (a) further comprises receiving, by the device, a command from a user to disable the configuration of the service.
 4. The method of claim 1, wherein step (b) further comprises identifying, by the device via monitoring, that the service has the status of down.
 5. The method of claim 4, further comprising excluding, by the device, the weight specified by the configuration for the service from the first sum of the health.
 6. The method of claim 1, wherein step (c) further comprises determining, by the device, the second sum of the health by summing each weight specified by the configuration for each of the plurality of service for which the configuration is enabled and the status of the service from monitoring is either up or down.
 7. The method of claim 1, further comprising determining, by the device, the health of the virtual server upon a change in one of the status of one of the plurality of services or the configuration of one of the plurality of services.
 8. The method of claim 1, further comprising determining, by the device, that the health of the virtual server exceeds a threshold.
 9. The method of claim 8, further comprising establishing, by the device in response to the determination, a second virtual server.
 10. The method of claim 9, further comprising directing, by the device, requests from the plurality of the clients to the second virtual server.
 11. A system of a device intermediary to a plurality of clients and a plurality of services to determine a health of a virtual server, the system comprising: a device intermediary to a plurality of a clients and a plurality of services executing on one or more servers, a virtual server established on the device and configured to manage the plurality of services, each service of the plurality of services has a configuration on the device that specifies a weight and whether the configuration is enabled or disabled; wherein the device is configured to identify via monitoring of the plurality of services, that a service of the plurality of services, with a configuration that is disabled, has a status of up; and wherein the device is configured to determine for the virtual server a health comprising a first sum of each weight specified by the configuration on the device for each of the plurality services that has the status of up divided by a second sum of each weight specified by the configuration on the device for each of the plurality of services for which the configuration is enabled, the second sum excluding the weight of the service with the configuration that is disabled.
 12. The system of claim 11, wherein the device is further configured to receive specification of the weight for the configuration of at least one service of the plurality of services from a user.
 13. The system of claim 11, wherein the device is further configured to receive a command from a user to disable the configuration of the service.
 14. The system of claim 11, wherein the device is further configured to identify via monitoring that the service has the status of down.
 15. The system of claim 14, wherein the device is further configured to exclude the weight specified by the configuration for the service from the first sum of the health.
 16. The system of claim 11, wherein the device is further configured to determine the second sum of the health by summing each weight specified by the configuration for each of the plurality of service for which the configuration is enabled and the status of the service from monitoring is either up or down.
 17. The system of claim 11, wherein the device is further configured to determine the health of the virtual server upon a change in one of the status of one of the plurality of services or the configuration of one of the plurality of services.
 18. The system of claim 11, wherein the device is further configured to determine that the health of the virtual server exceeds a threshold.
 19. The system of claim 18, wherein the device is further configured to establish, in response to the determination, a second virtual server.
 20. The system of claim 19, wherein the device is further configured to direct requests from the plurality of the clients to the second virtual server. 